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THE SITUATION ROOM

Boston Bombing Investigation Continues; Suspicious Letter Sent to Senate; Photos Show Bag Near Bomb Site; Hunt for Clues in Marathon Bombings; Vigil Tomorrow for 8-Year-Old Victim

Aired April 16, 2013 - 18:00   ET

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.


WOLF BLITZER, CNN HOST: Investigators say the hunt for a suspect is still wide-open. They're asking the public for help.

Gut-wrenching stories of young lives cut short. The mother of a 29-year-old victim speaking out just a short while ago.

And we're reconstructing the scene of the bombings to show you exactly what investigators are looking for and the places where clues may be hidden right now.

I'm Wolf Blitzer in Boston. We want to welcome our viewers in the United States and around the world. This is a special edition of THE SITUATION ROOM: the Boston Marathon bombings.

Here in Boston, we're seeing a lot of raw emotion and determination to honor the victims of the marathon terror attack and to find out who is responsible. If you're just joining our team coverage, here are some of the latest developments.

Investigators have just confirmed publicly that the bombs used in the attack were likely placed in pressure cookers, and then hidden in a nylon bag or backpack. They're asking witnesses who may have seen someone with a bag like that to contact them as soon as possible.

President Obama will travel here to Boston on Thursday for a religious interface service dedicated to the three people killed in the attack and the more than 180 people injured. We now know the name of another of the three people who died, her name Krystle Campbell. She was 29 years old. Her mother spoke out a little while ago in tears, saying she and her family are heartbroken.

And we also just learned that the third person who died was a Boston University graduate student. We will bring you more when we get it.

Investigators here in Boston say their hunt for a terrorist -- for a suspect in these terror bombings is still preliminary, and this case, they say, is wide-open.

(BEGIN VIDEO CLIP)

RICHARD DESLAURIERS, FBI SPECIAL AGENT IN CHARGE: Among items partially recovered are pieces of black nylon, which could be from a backpack, and what appeared to be fragments of BBs, and nails, possibly contained in a pressure cooker device.

In addition, this morning, it was determined that both of the explosives were placed in a dark-colored nylon bag or backpack. The bag would have been heavy because of the components believed to be in it.

(END VIDEO CLIP)

BLITZER: Let's bring in our chief national correspondent, John King, who is working his sources, doing some serious reporting on what's going on.

It's clearly a preliminary stage, at its infancy, the FBI agent in charge says of this investigation.

JOHN KING, CNN CHIEF NATIONAL CORRESPONDENT: Only a little over a day old, this investigation. But you do start to sense a bit of frustration from sources you talk to in private, and at that public briefing we just heard, you heard the FBI special agent in charge, he used the term infancy and he also made a public appeal asking anyone who might think, would have any slightest clue, did you know anyone who might have had a big black nylon bag or a backpack, who might have said something disparaging about the marathon or some plan to come down here to attend the marathon?

Clearly, what I'm told by sources, at the public briefing they said there were no suspects as yet. What I'm told by several sources in private is there a frantic review of the video evidence under way. There are some gaps in the forensics so far in terms of they have video images of the sites where the explosions are. Possible video images of the devices on site. No video at least in the conversations just a short time ago showing any suspicious person or persons dropping a package and trying to leave.

That is the appeal for public help, did anybody say anything, does anyone have any image that might help the FBI in this investigation? You heard the special agent in charge say part of the debris, including what he believes to be fragments from pressure cookers sent to the Quantico FBI lab laboratory, where they will try do just as they do after an airplane plane, essentially try to put together and reconstruct the plane, in this case reconstruct the explosive device, and then hope they can find a fingerprint, DNA, some signature that might lead them to an individual or to an organization.

I can tell you, though, at this point, Wolf, all the sources I have talked to, they say this is not a bluff, that they have no suspect identified so far. They had a Saudi national identified as a person of interest. They conducted a search of his apartment and they said that individual has been cleared, just in the wrong place at the wrong time.

You have now in the second full day of the investigation, thousands of federal, state and local authorities. The crime scene right over there, the restricted area was 15 blocks, it's been cut down to about 12 blocks now. But essentially they're still looking, and you heard the ATF representative at that news conference say they're finding debris up on rooftops, and also embedded into buildings, trying to get all of that evidence again to try to rebuild and try to find clues.

But clearly when they make a public appeal for help like that, it tells you at this point in the words of the Boston police sources I spoke with a few hours ago, they're stymied.

BLITZER: And that forensic lab at Quantico in Virginia, the FBI lab, they're going to try to piece together as much as they can to see if it fits other bombs that they may have seen, whether here in the United States or elsewhere around the world, explode over the years.

KING: And our terrorism experts can do a better job than I can, but it makes the investigation, at least in this infancy stage as they described it, so difficult, in the sense that this is a relatively crude device.

Yes, a device that has been used by al Qaeda, used by the Taliban in the past, but, but I want to stress this, from all of our sources, from all of our reporters, producers and correspondents, zero evidence, zero evidence of any communications, any intelligence suggesting a foreign terrorist involvement as yet.

And even though this has been used, this type of technology has been used by al Qaeda and the Taliban in the past, it is also sadly in this age of the Internet a technology where you can go online and essentially find a how-to to build a bomb like this. And so no one has ruled out domestic terrorism, no one has ruled out this being a single lone wolf bomber, perhaps someone with help. They say right now those are among the many, many questions.

BLITZER: And it's significant also that no one has claimed responsibility. There's almost a thunderous silence, if you will. That speaks volumes to a lot of these investigators.

KING: If you look past backwards, at past terrorist attacks, obviously if it's al Qaeda, if it's al Qaeda in the Arabian Peninsula, if it's some political group, even a domestic political group trying to make a point, often there's a claim of responsibility within the first day or two. The silence is again part of the investigation, and a reminder to us that what is not being said and what we don't know is perhaps much more important than what we do know.

BLITZER: All right, John, don't go too far away.

Just moments before the terror attack here in Boston, 29-year-old Krystle Campbell was waiting at the finish line at the marathon to cheer on the runners. Now she's dead. Her identity was confirmed only a few hours ago.

Jason Carroll is in the Campbells' hometown of Medford right outside of Boston.

Jason, tell us what is going on. What are you learning?

JASON CARROLL, CNN CORRESPONDENT: Just a terrible story here, Wolf, like so many other stories.

Just a little while ago, Patty Campbell came out on her front porch, she tried to speak about her daughter, but she was so overcome by grief, she just simply couldn't do it. And their story is just a tragic case of a mix-up.

Let me explain a little bit more about what happened to Krystle Campbell. As you said, she went out to watch the marathon. She got caught in the first explosion. And then, Wolf, shortly thereafter, taken to the hospital, and her parents were told that she was OK, that they were working, trying to save her leg.

Shortly after the operation, her parents came into the room and learned it wasn't her at all that had survived. It was her friend. So you can imagine how terribly awful they feel at this point, how they're trying to deal with the loss of their daughter, trying to deal with this tragedy. Again, just a short while ago, Patty Campbell came out, tried to speak to the press, but eventually a spokesman had to say what she simply could not.

(BEGIN VIDEO CLIP)

PATTY CAMPBELL, MOTHER OF VICTIM: We're heartbroken at the death of our daughter, Krystle Marie. She was a wonderful person.

Everybody that knew her loved her. She loved her dogs. She used to -- she had a heart of gold. She was always smiling. I couldn't ask for a better daughter. I can't believe this has happened. She was such a hard worker at everything she did. This doesn't make any sense.

QUESTION: What kind of daughter was she, ma'am?

CAMPBELL: She was best. You couldn't ask for a better daughter.

BRIAN KENNY, CAMPBELL FAMILY SPOKESMAN: And this statement is from Patty Campbell, the mother of Krystle Campbell.

"We are heartbroken at the death of our daughter, Krystle Marie. She was a wonderful person. Everyone who knew her loved her. She was sweet and kind and friendly, always smiling. She worked so hard at everything she did."

(END VIDEO CLIP)

CARROLL: And Wolf, just a short while ago, I reached out to Massachusetts General Hospital, just trying to get some clarification about what the Campbells are saying, what happened to their daughter.

A spokeswoman telling me they're still in the process of gathering information, trying to determine exactly what happened before they could release a statement. But it just goes to show you, in -- just in the hours after what happened, there was so much confusion, in some ways. Even some of the most experienced trained doctors, things like this can happen -- Wolf. BLITZER: Can't tell you how awful it must be, how awful for Patty Campbell, the mother of Krystle Campbell. It's shocking to me that she could even go out there and even try to make a statement.

I know she tried. And our heart, of course, go out to her, to the entire family, the families of the other victims, those who were killed. They were all so young, a young boy, Krystle Campbell. Now we have learned a graduate student at Boston University.

Jason, I don't know how people cope under these circumstances. And so many others, so many dozens of others of parents and family members and friends, they know -- those who are seriously, critically injured, losing limbs -- this is such a horrendous situation. It makes no sense whatsoever. And investigators are trying to figure out what happened.

CARROLL: That's exactly right.

And imagine, Wolf, the relief at first when you find out that something like this has happened to someone in your family, and then in a sense you're relieved that at least they're OK. And then it becomes the worry as you're hearing that doctors are working, and in this case trying to save her leg.

And then, of course, you're dealing with the grief upon learning about what really happened and then in a sense, some anger as well, trying to sort out how something like this could have happened. It's all of the emotions that this family is trying to deal with.

BLITZER: Please send our love to the family, if you have a chance to speak with them over there in Medford, Jason. Thanks very much for that report.

CARROLL: Absolutely.

BLITZER: Such a sad story indeed.

And to our viewers, if you're looking for ways to help people affected by the Boston bombings, go to CNN.com/impact. And a lot of good opportunities to do something positive as a result of this horrendous, horrendous tragedy.

Let's take a closer look at this these terrorist bombings.

CNN's Tom Foreman and CNN analyst Tom Fuentes, a former FBI assistant director, are both standing by.

Tom Foreman, give us a little sense of what's going on here as far as this investigation is concerned.

TOM FOREMAN, CNN CORRESPONDENT: Wolf, Tom and I have been talking all day long about three critical time periods that have to be considered in all this.

Let me bring in the crime scene so we can talk about what we mean. First critical time period, the actual time of the explosion. We know that about 17,000 runners had already crossed the finish line on Boylston Street, another 6,000 were headed that way when the first big bomb went off. They're just short of the finish line. And about two football fields away, 12 seconds later the second bomb went off.

Obviously those sites, Tom, are critical to investigators in terms of physical evidence. What are they looking at right now?

TOM FUENTES, CNN CONTRIBUTOR: Tom, the first thing they want to do is recover as much of the bomb device as they can, to help identify who may have made it, how it was constructed, and get an idea whether right there it would help focus whether it's international or domestic, or a group that's been seen before by the way it was put together. So first issue is get pieces of that bomb, as much evidence of the explosive device, and the material contained in the device as they can.

FOREMAN: And we have been hearing bits and pieces about that all day, about like a nylon bag, that sort of thing.

But let me rotate the table around here because I want to show you something here. The expanded search area is actually much bigger than the initial explosion, Tom. They just didn't focus on the initial area, but really for a couple blocks around. Why so far?

FUENTES: The materials in the bomb are exploding and traveling through the air at about 7,000 feet per second. You could easily have material from the first bomb overlap material from the second bomb. So literally you could find a detonator near the second bomb that maybe came from the first bomb.

So, you have this tremendous amount of debris that could possibly overlap, depending on the position of the buildings, and...

(CROSSTALK)

FOREMAN: You could have a critical part that was blown up onto, for example, one of the rooftops that may be a block away.

(CROSSTALK)

FUENTES: This is the one of other first places they looked. This is very common in an explosion to have parts of the bomb go airborne, straight up and over the top of buildings. They even land blocks away.

FOREMAN: Let's talk about the second critical time here. The second critical time is the time right before the race.

Let's change all these pictures to what was happening them. There were happy families, people gathered all around. There had been a sweep for explosives just three hours before this went off. So, Tom, they're looking at photographs, they're looking at video, they're talking to all these people and saying, what did you see that maybe at that time did not seem like a big deal?

FUENTES: Right. You had people coming and going all during that time.

And again, the belief that timers were used for the device, so somebody could have come there and put the device down and walked away a long period of time, let's say, before the bomb exploded. I don't think they would have done too long a time maybe fearing that maybe dogs would come along and locate the device and neutralize it.

So probably the period of about 30 minutes up to the time of the explosion would be the critical time. But from a video and witness standpoint, the police would want to be looking back to several hours if they can to see if somebody was there a longer period of time or came and went a couple of times.

FOREMAN: One other really critical thing -- and this is very different in this crime scene compared to many others, Wolf, the simple truth is, every single runner in this race coming down that chute was wearing an electronic tracking tag, so that the race organizers would know where they were.

The runners are busy running. They really don't have time to be looking at the sidelines. But they still matter. Why?

FUENTES: Well, the important thing is that the runner probably has family members, friends, neighbors, colleagues, who are on the sidelines to support them.

So, by knowing who crossed that line at the certain time, you go to the runner and then ask them about who else was there with you, and we would like to interview them and see if they have photographs.

(CROSSTALK)

FOREMAN: Phone numbers and e-mails and everything else. The last critical period of time of course is what happened before and after that, whether or not somebody was in a restaurant, whether somebody was in a parking garage or captured by another security camera some distance away.

Did they see something that will lead to the fourth critical period of time, Wolf, and that is, an arrest -- Wolf.

BLITZER: Yes, Tom Foreman, Tom Fuentes, guys, thanks very much for that analysis.

The FBI agent in charge says this investigation is in its infancy right now.

Up next, video from the crucial moments while the marathon was under way, before the attack, what investigators are looking for in every image. We will assess for you.

And you may have seen the video, a man blown off his feet when the bombs went off. He's telling his dramatic story.

(COMMERCIAL BREAK)

BLITZER: There is a very, very disturbing report coming out of Washington, D.C., right now. I'm here in Boston.

But our chief congressional correspondent, Dana Bash, is joining us on the phone right now.

And I want to be precise, Dana. Tell our viewers here in the United States, and around the world, what you're learning.

DANA BASH, CNN SENIOR CONGRESSIONAL CORRESPONDENT: Well, CNN has learned, Wolf, that an envelope that was addressed and sent to a Senate office was intercepted and tested positive for ricin poison, ricin poison.

And I have learned that from congressional and law enforcement sources, myself and Mike Brooks, who actually got the first tip on this story. Now, we don't know which Senate office this was originally sent to. But we do understand that this envelope was tested positive in a first routine test. It was retested two more times, so it was tested three times altogether.

Each time, it came up positive. And that's according to a law enforcement source who said that afterwards it was sent to Maryland on an off-site facility to do further testing. We should remind our viewers that after the anthrax scare back in 2001, in the fall of 2001, when a couple of Senate offices received envelopes with anthrax in it, they changed the way that the mail is distributed on Capitol Hill, so they now begin for the most part off-site.

So this was intercepted at an off-site mail facility. It was not done -- it did not make its way to the Capitol. So this is the information that we have so far. I can also tell you that Ted Barrett, CNN's congressional producer, asked Senate Majority Leader Harry Reid about this, what we were learning, and he simply responded, rather sternly, according to Ted, "I am not going to comment on that, end of conversation."

And we should also tell people who maybe aren't that familiar with ricin, it is highly poisonous, even in small quantities. It's actually a poison that is made from caster beans.

BLITZER: Hold on for a moment, Dana, because I want to bring Fran Townsend into this, the former homeland security adviser to President Bush, our homeland security analyst right now.

As Dana said, it's highly poisonous, ricin, this letter that has apparently been tested three times, Fran. Give us a little sense, a little sense of proportion what this potentially means.

FRANCES TOWNSEND, CNN NATIONAL SECURITY CONTRIBUTOR: Well, Wolf, it's deeply concerning, because just as we have told our viewers, that the pressure cooker-type construction of an explosive device has been touted on al Qaeda Web sites, the use of ricin as a poison, there have been cells.

One that comes to mind for me just off the top of my head was in the U.K. But there are al Qaeda manuals that talk about the use of ricin, and the deployment ricin as a poison. And so, look, we don't know where the envelope came from. We don't know the threat. We haven't identified the source of the bombing in Boston.

But these are -- each of these has got some history, some tie sort of to the al Qaeda playbook, if you will, and I have no doubt that that's in the investigators' mind as this news breaks.

BLITZER: Fran, hold on for a moment. Dana, hold on for a moment, because there's other breaking news we're following right now as well.

Let me a tribute this to our affiliate WHDH here in Boston. I want to show you exactly what they are now reporting. These are photos, two photos sent to WHDH by a viewer. Shows the scene, the first one shows the scene just before, and the other one shows right after the bombs went off on Boylston Street.

You see this first photo here. You see a black bag there along the streets. And then you see afterwards, at virtually the same location, the explosion. You see these bags. WHDH says they have provided these pictures to the FBI as they continue their investigation. They're looking at the pictures to see if it's possible it could be the second bomb.

In the first picture they say you can see a bag next to a mailbox, and up against the barricade along the marathon route. In the second, which they blurred because it's very, very graphic, there is no sign of the bag, that from our affiliate WHDH, the FBI now investigating these photos to see if in fact that is the bag that contained the bomb with the pressure cooker device.

Fran, let me bring you back in. Assess what WHDH is now showing.

TOWNSEND: Well, Wolf, what will happen is, the FBI, in particular, and the forensics lab at Quantico will take these photographs, the fragments that have been sent to Quantico, and this is the painstaking process.

When the chief of police in Boston says this will be methodical and they will be cautious, this is the sort of painstaking investigative steps. They will try to measure up fragments, small fragments of what's left to what they see in these photographs, and try to see what they can learn in particular about the construction of these specific devices.

They will then try to see what they can learn about the device that's not pictured from the other bomb site in Boston. They will look for things like fingerprints, DNA samples. You may find DNA samples of victims, Wolf, but you also may find DNA samples, hair and skin samples from the bomb maker himself. Those are the sorts of details that they will begin to try and get from the crime scene, the forensics and photographs such as these.

BLITZER: It's very disturbing, because in that first picture before, you see this bag outside of the barricade right next to that mailbox.

John King is here. And we're looking together at this photo. And you say to yourself, why would they let a bag stay outside the barricade like that in an open area, where the marathon is coming to a conclusion?

KING: This is one of the questions, and the police commissioner was asked about this, are you confident about your plan, did you have lapses in security at the finish line?

One of the things investigators are now looking at is you have a larger crowd packed in there when the elite runners cross. And then the crowd shifts a little bit. That people who are there, the dignitaries who are there to watch the elite runners, they're there.

And then this was well after that, about two hours after the elite runners cross. There's a more fluid situation, people are moving about. One of the questions is as the crowd shifts, and as the crowd changes and as the pressure is off, if you will, that you have your everyday marathoners crossing at the four-hour mark, did the security people let their guard down?

Obviously, the police commissioner said that is something they will deal with after the fact, that the focus is now on the investigation. But there's no doubt as they look at these photos, and we talked about this earlier, I have talked to a Boston police source who said there's a frantic review of these photos, and this source told me without being specific about these shown by our affiliate WHDH, that they do believe they have some possibles -- possibles was the term he used on the devices in the locations of the explosions.

What they did not have in that conversation just a short time ago this afternoon, this source told me was any evidence, video evidence so far of a drop or a placement. So this is part of what Fran calls, and the police officers have called the methodical review.

But if that happens, someone was able to, while the runners are still crossing the finish line -- again, these are your everyday marathoners, not the elite runners, but if someone were able to get that close with a bag that big unnoticed, no doubt about it, there will be questions about a security lapse.

BLITZER: Let's ask Tom Fuentes, the former FBI assistant director, a CNN contributor right now, what's your assessment of these two photos?

FUENTES: Well, I agree, Wolf, that they're going to have to be analyzed in detail to determine exactly what we have.

It looks bad as it is. But I would like to hear more results of analysis to determine what we have.

TOWNSEND: Wolf, it's worth noting for our viewers what we're looking at in both the before and after photographs of this that we have gotten from our affiliate, there will be hundreds of frames in between.

(CROSSTALK) TOWNSEND: And before the picture that -- the first picture of the bomb and the afters, they will go frame by frame through these to try and extract every bit of forensic intelligence they can get to identify the bomber.

BLITZER: As you take a look at these pictures right now, walk us through, Tom Fuentes, walk us through how the FBI would go through this process of trying to assess if in fact this is the bag that contained one of the two bombs.

FUENTES: Well, certainly they will be taking the physical evidence that's been recovered from the debris at the crime scene, and try to determine if it would match what we see in the photograph, at least as near as they can tell, without having the two things together.

But they're going to be looking at these photographs, as Fran mentioned, in detail, and looking at the sequence of the photographs, and the timing of them, and try to determine from that what the likelihood is of the match.

BLITZER: Would it be normal to just have a bag lying there outside of the barricade close to the runners like that? Wouldn't some local law enforcement type notice that, and raise some suspicions, get a dog over there to sniff it?

FUENTES: Well, possibly.

But you have -- you know, you have people showing up there to be with their loved ones, and colleagues who are in the race, and may be carrying backpacks, and may have been there a long time and placed backpacks down because they're heavy.

So you have everybody there, or a large number of people there with backpacks, and many of them taking them off, setting them down because they're heavy, moving them around. And most of the people are focused on the runners and in the people in the crowd and aren't necessarily paying attention to each individual bag that gets left.

It's not the same as an airport, where they say unattended bags will be picked up and possibly destroyed. Here, you have so many bags laying around and people talking and milling around, moving away from the bags, that it's a little bit harder to determine the suspicion of a particular bag lying around.

KING: Tom, we heard the FBI agent in charge, Rick DesLauriers, say at this news conference a little while ago they believe the bombs were placed in what he described as black nylon bags or backpacks. He used the word backpacks, also bags.

If there is a bomb and it explodes, how do they know -- wouldn't that bag be destroyed in the course of that explosion?

FUENTES: No, you know, interestingly, in an explosion like that, almost none of the elements, whether it's the bag, the containers, the bomb itself, almost none of them are completely destroyed or vaporized. They tend to be fragmented, and the fragments get exploded airborne, and pieces of that nylon would be embedded in spectators' clothing that were nearby, or may end up in -- just on the sidewalk as part of the debris.

So -- so in most of these cases, they'll be able to reconstruct the material that that bag was made out of. Maybe even the brand of the bag, if they get a piece of the label, or some other logo from the bag. Same thing with containers inside. And what was used to actually hold the explosive, and hold the shrapnel. All of those things will be recoverable if they can find them, and if they can, you know, piece together that that probably came from the device, and wasn't just part of the other trash that was in the area that got spread around.

BLITZER: I'm sure they'll be looking closely at these -- this image to see if, in fact, they blow it up or whatever, if they expand it, to see if it is, in fact, a black nylon bag, or something else.

All right. Everybody stand by. It's the bottom of the hour. I want to update our viewers. If you're just joining our team coverage here in Boston, here are some of the other latest developments we're following right now.

Just a few minutes ago, the third victim killed in the marathon terror attack was identified as a graduate student at Boston University. The name is not yet being released.

Also, investigators now say they believe the bombs were made from pressure cookers filled with BBs and nails designed to cause maximum carnage.

President Obama's planning to visit the shaken city of Boston. The Massachusetts governor, Deval Patrick, said the president will be here to participate in an interface -- interfaith service Thursday morning, 11 a.m. Eastern.

We're told that law-enforcement officials here in Boston are now combing through hundreds, hundreds of pictures and videos. They're looking for clues about the Boston Marathon bombings and possible suspects. And they're appealing to the public for help.

(BEGIN VIDEO CLIP)

RICK DESLAURIERS, FBI SPECIAL AGENT IN CHARGE: Someone knows who did this. Cooperation from the community will play a crucial role in this investigation, and we are asking the public to remain alert, and alert us of the following activity.

Any individual who expressed a desire to target the marathon. Suspicious interest in researching how to create explosive devices. The noise of explosions in remote areas prior to yesterday, which may have been used as tests by those responsible for these acts. Someone who appeared to be carrying an unusually heavy, dark-colored bag yesterday around the time of the blasts and in the vicinity -- vicinity of the blasts.

(END VIDEO CLIP)

BLITZER: Brian Todd is here with me in Boston. You've been some investigating. What are you picking up?

BRIAN TODD, CNN CORRESPONDENT: Well, Wolf, on the one hand, encouraging signs, because we're getting new clues. The new pictures we just saw, possibly of the bombs, new information on the materials used in it: BBs, nails, nylon.

On the other hand, though, still no suspects. And potentially thousands of frames of surveillance and other video to comb through.

(BEGIN VIDEOTAPE)

TODD (voice-over): Investigators are combing through what Boston's police commissioner calls the most complex crime scene in his department's history. What makes it so difficult? It's two crime scenes, two separate blasts, police officials say. Debris and people were everywhere. Could clues come from the so-called explosive ordnance disposal sweeps that were conducted before the bombs exploded?

ED DAVIS, BOSTON POLICE COMMISSIONER: There were two of them done that morning. One was done early in the morning, and a second one was done an hour before the first runners came across.

TODD (on camera): That means the time between the last ordnance sweep of the finish line area and the first blast was about 3 hours and 40 minutes. Now, those sweeps are not airtight, so there's a chance the bombs could have been planted before the sweeps took place. But if they weren't, that still leaves a large swath of time in an open area with a lot of people around that investigators have to examine to find possible suspects.

(voice-over): Investigators say they need specific evidence to find who's responsible. From surveillance tape, video and still pictures from private citizens and media outlets. Boston's mayor told me this about the area of the finish line.

MAYOR THOMAS MENINO, BOSTON: We have cameras on -- probably the most heavily cameraed neighborhood in the city of Boston. We're looking for those. A lot of those businesses along Boylston Street have their own cameras for safety reasons also, for theft of their store.

TODD: Google Earth street view shows the area near the second blast. Merchants like the Atlantic Fish Company restaurant, Crate & Barrel and Starbucks that could offer surveillance video.

Former assistant homeland security secretary Juliette Kayyem explained how surveillance can be pieced together with private video or stills.

JULIETTE KAYYEM, FORMER ASSISTANT HOMELAND SECURITY SECRETARY: You may look at a picture that you took and think, "Oh, there's my dad finishing the race," and in the background there's a guy, and he looks like he's doing something normal. But if someone else has a picture four seconds later where he's dropping off a bag that that looks sort of strange, and then four seconds later there's another picture that shows him running, then you -- it doesn't end up being that easy, but that's how you put the pieces together.

TODD: But that's not so straightforward, either.

PROFESSOR JAMES FOX, CRIMINOLOGIST, NORTHEASTERN UNIVERSITY: It could be that the behavior itself doesn't look suspicious, something's in a bag, they don't know what it is. It could be innocent. Or it could be that there's a camera shot, but someone walks in front of it, and you can't see the perpetrator leaving a bomb behind.

(END VIDEOTAPE)

TODD: And again, new information tonight as to the kind of bombs being used, possibly in this attack. Law-enforcement officials saying that the bomb materials, the bomb packs had BBs, nails, nylon in them. Possibly black backpacks used, black bags used.

New information, Wolf, and as we heard Susan Candiotti report earlier, what they reaffirmed in the news conference, they could have been packed in some kind of a pressure cooker type bomb.

BLITZER: Are you getting new information also on what the scope of this explosion?

TODD: That's right. Law-enforcement officials now saying that they found debris on the rooftops nearby. They found some debris from the bombs embedded in buildings nearby. Tom Fuentes said a little while ago this type of explosive -- explosion carries about a 7,000 feet-per-second force. So that just gives you an idea of the scope. Debris on rooftops nearby. You know, some of these buildings are very tall.

BLITZER: It proved that it was deadly and powerful, to be sure. Brian, thanks very much for that report.

Still ahead, we're getting new information on a letter sent to the United States Senate that has tested positive for the poison ricin. Stand by.

(COMMERCIAL BREAK)

ANNOUNCER: This is CNN breaking news.

BLITZER: There are so many developments happening right now. But there's an important one happening in Washington, D.C., in the United States Senate. Our chief congressional correspondent, Dana Bash, has been reporting on the breaking news. A letter apparently laced with the poison ricin was sent to a United States senator.

This is a deadly poison, Dana. What are you picking up?

DANA BASH, CNN CORRESPONDENT (via phone): Well, we can now report that the senator to whom this letter was addressed is Roger Wicker, Republican senator of Mississippi. And, you know, we reported this news before most senators even knew that Senator Wicker had received this letter, which, again, has tested positive three times for the poison ricin.

But as we were reporting it, there was a meeting of all senators. They're actually getting briefed on the developments in Boston. But while they were there, they were also told about this letter that went to Senator Wicker. And what some senators coming out told our Rachael Stritefeld (ph) Ted Barrett, our congressional producers, is the following.

First of all, Senator McCaskill has said that she -- her understanding coming out of this briefing is that there might even be a suspect in custody. The suspect is somebody who, according to McCaskill, quote, ?"writes a lot of letters."

But she also emphasized something that we reported earlier, and you know, this should be underscored, that this was caught at a screening facility. Meaning, the letter that may have ricin in it, the poison ricin, did not come to the U.S. Capitol. And the reason for that is because the process changed dramatically after anthrax was sent, back in 2001, to two offices in the U.S. Senate. So now they're done offsite.

And it was at that offsite facility that this letter was test -- tested positive for ricin three times. And just to update our viewers, as we speak, that letter is at yet another facility in Maryland, getting another test just to be sure that it is, in fact, the poison ricin.

BLITZER: And just to be precise, Dana, one letter discovered so far, only one letter sent to Senator Roger Wicker. Did you say that we have a statement from Senator Wicker's office?

BASH: We do not have a statement from Senator Wicker's office yet, but what happened was, because all senators happened to be attending a briefing on developments in Boston, they were in the presence of the FBI director, the homeland security secretary and others, who used the opportunity to tell them about this news that we first reported on CNN.

And during the course of that briefing, according to one senator who was there, Senator McCaskill of Missouri, she said that her impression is that there might even be a suspect in custody, who may have sent this letter. But we're going to obviously try to dig deeper on that and get more information.

BLITZER: As soon as we get more, Dana, you'll share it with our viewers. A disturbing development. Brings back memories of anthrax, those letters back in 2001, after 9/11 that were sent out to members of Congress, members of the media, and others. Dana will check her sources and get more information.

Meanwhile, all over this city of Boston and across the country, relatives of the bombing victims, they are in shock. In some cases more than one member of a family has been hurt. We're joined on the phone now by Jocelyn Wood-Garrish. Her two cousins were injured in the attack. And they are in the hospital.

Jocelyn, how are your cousins doing?

JOCELYN WOOD-GARRISH, FAMILY MEMBERS INJURED IN BOMBING (via phone): Hello, Wolf. One cousin, she's had a lot of coverage on the news, locally -- locally for sure, she's in critical condition. She has extensive leg injuries. She's undergoing second and possibly a third surgery today. I know that -- I know that that won't be the last surgery, they're saying. They are hoping that she'll be OK. But for now, she's in critical condition. And that's pretty much all they're saying. It is -- it is pretty grave.

Nicole, she is now in stable condition, and she also has leg injuries. Not quite as severe. She's in and out of consciousness and has been able to talk at times. Her husband is Michael, and they're both from Charlotte, North Carolina. He has been technically discharged today. He had lacerations and severe burns, from what I was told. But he has been discharged. So I'm sure he's by Nicole's side, along with my Aunt Carol Downing, and my uncle Skip Downing, as well.

BLITZER: Your aunt was, what, running in the marathon, is that right?

WOOD-GARRISH: Yes. My Aunt Carol was running in the marathon. She's been running the marathon for years, as has Nicole, and recently Erica has started running in the last two years. But this particular trip, Erica and Nicole and Michael just went up to support her. So they were, from what we know, they were on the sidelines, obviously, pretty near one of the blasts.

And it seems the two girls, Nicole and Erica, were a little closer together, where Michael was a little further away from them, because he had, like I said, burns in his trachea, and on his body. So he had a different experience, outcome than the girls.

BLITZER: Jocelyn Wood-Garrish, please, please send along our best, our love to all of those -- all of those loved ones who have been so seriously injured in this horrendous bombing here in Boston. Jocelyn, thanks for sharing a few thoughts with us.

Anderson Cooper is standing by here in Boston. I'm going to be speaking with him in a moment. He has just wrapped up a conversation with another bombing survivor in a hospital.

(BEGIN VIDEO CLIP)

RON BRASSARD, INJURED IN BOMBING: On the news today we saw where the explosion occurred. And I was right in front of, like, the Lenscrafters.

(COMMERCIAL BREAK)

BLITZER: Anderson Cooper's here in Boston. He's been doing some reporting. He's just spoken to someone who really is going through hell right now. ANDERSON COOPER, CNN ANCHOR: Ron Brassard, he was at the race with his wife, about ten feet away, he believes, from the first explosion. I talked to him about what he saw and heard. Take a look.

(BEGIN VIDEO CLIP)

BRASSARD: There was just this explosion, and very, very nearby. I mean, it was so close that you couldn't hear after the explosion.

COOPER: Really? You couldn't actually hear anything?

BRASSARD: I couldn't -- I could see people's mouth moving and stuff, but I couldn't hear anything.

COOPER: How close were you to the first bomb?

BRASSARD: I think we were probably about ten feet away. When we saw, on the news today, we saw where the explosion occurred.

(END VIDEO CLIP)

COOPER: His wife was injured, as well. He was badly injured in the leg, a lot of blood loss, but he's doing OK, and his wife is doing OK, as well.

BLITZER: It makes no sense. Are people saying why? Why, why? Because that's what I keep hearing.

COOPER: You know, he's really kind of resolute and stoic in the face of all this and really doesn't want to live in fear. And that's sort of one of the message that we're going to talk to him about tonight on 360, is that, you know, he doesn't want this to alter his life. And he feels, obviously, very lucky that the wound could have been much worse, and he knows somebody who has lost a limb. He knows other people have -- have suffered a lot worse.

BLITZER: So many have, and so many children, too. It's so heartbreaking.

COOPER: Yes.

BLITZER: Anderson, 8 p.m. Eastern, we'll be watching "AC 360." Thanks very much.

So here in Boston, I've also been talking to people who survived the deadly terror attack on this city, more witnesses, more victims. They are coming forward today with very emotional stories.

(BEGIN VIDEO CLIP)

UNIDENTIFIED MALE: Smoke and debris everywhere. Across the finish line, screams, people running.

UNIDENTIFIED MALE: People panicked?

UNIDENTIFIED MALE: Oh, yes, extreme panic. BLITZER (voice-over): You can see it and you can hear it. Marian Shugas (ph) was sitting in the VIP area near the finish line. The first bomb went off to her right, the second to her left.

UNIDENTIFIED FEMALE: Say a prayer, say a prayer.

BLITZER: The explosion hurt spectators as well as runners. A woman from New Hampshire was walking past a restaurant when the blast went off.

DENISE SPENARD, INJURED IN BOMBING: I felt something sharp. I hadn't even looked at it yet. And then, when I got inside, when we -- before we were trying to get under the table, I had pulled up my sweatshirt and then at that point, I realized that I was bleeding. And although I didn't know it was from the explosion. I thought I was shot or something. So...

UNIDENTIFIED FEMALE: Can you show us the wound? Do you feel comfortable?

SPENARD: I mean, you can't really see it. It's under there.

UNIDENTIFIED FEMALE: And it's bloody.

SPENARD: Yes, it is.

BLITZER: We saw this video again and again. The man literally blown off his feet is 78-year-old Bill Iffrig. He told his story to CNN's Piers Morgan.

BILL IFFRIG, MARATHONER: A tremendous explosion, sounded like a bomb went off right next to me. And the shockwaves just hit my whole body, and my legs just started jittering around. I knew I was going down.

BLITZER: What you don't see in the pictures is Iffrig got off and, with a little help, finished the race.

IFFRIG: I felt OK, so I told them, "I'll be all right," and he insisted on getting a wheelchair over there, so we started to do that, but then before they had one rounded up, I said, "Hey, I'm only -- my hotel is about six blocks away so I think I can make it OK." So they let me get out of there, and I went on home to my wife.

(END VIDEOTAPE)

BLITZER: Good for him. Thankfully he managed to finish, and he's OK.

Still ahead a tribute planned for the 8-year-old boy killed in the Boston bombings. We're hearing from his father about his family's excruciating pain.

(COMMERCIAL BREAK)

BLITZER: We're back here in Boston. Our live coverage of the marathon terror attacks continues in THE SITUATION ROOM.

A candlelight vigil is planned for tomorrow night for the 8-year- old, Martin Richard. The boy's death and his family's injuries have touched all of us. They've touched people all over the world.

John King has got the story, and it's such -- such a sad story. What happened?

JOHN KING, CNN CORRESPONDENT: Wolf, this one hits too close to home, if you will. I grew up in the very neighborhood where 8-year- old Martin Richard did. It's in Dorchester. It's a blue-collar neighborhood. I was at St. Ann Parish today. In Dorchester, when people ask you where you're from, and in Boston, you identify your parish, even if you're not a Catholic. You identify the Catholic church and the parish. I grew up in St. Mark. This is St. Ann, about a mile away.

An 8-year-old boy, he attended the Catholic school. Then he went to this community charter school. We went to the charter school today, where his mother, who is still hospitalized, is a librarian. His younger sister, a first-grader, who's an Irish dancer, she lost one leg yesterday in an explosion. I was told she may have to lose her second leg to be kept alive. She is still hospitalized.

Her father, Bill, was there. He is OK. He was meeting with the pastor in the church all day long. I'm told he's in shock. They have a 10-year-old son, as well. It's so eerie. You go to this charter school. I grew up on King Street. The charter school is on Queen Street which intersects with King Street. It was up a little hill.

In the parking lot of the school, where students today inside were getting counseling, you look up and what do you see? You see the Prudential Tower and the Hancock Tower. You see Copley Square. A vision from this school, an eerie look of the very site of the finish line where this 8-year-old boy was the youngest of the three fatalities in the crash [SIC].

I grew up in the community. My paper route was right through this -- this current neighborhood, where his parents live. They grew up on the other end of Dorchester, his mother did, in Savonville (ph) area. It's just -- people are just stunned. They're stunned by the scope of this attack, but especially, as we felt after Newtown, as well, that an 8-year-old has to be among the fatalities.

BLITZER: The 8-year-old is dead. His sister is in critical condition, has lost a leg, maybe will lose another leg. The mother is in bad condition, as well. Serious head injuries, right?

KING: And a leg injury to her, as well. Denise -- Denise Richard is the mom. She was -- worked for the state department of transportation. It was called Mass Highway at the time, for ten years, when she was pregnant with the third child, the young girl. She has a boy, Henry, the deceased boy, Martin, and then the girl, Jane, who's 6 years old, a first grader. When she was pregnant, she left the state employment. She was at home for a couple of years, and then she took a job at the library of this charter school. It's a small in the community. It's a close-knit, blue-collar community, triple decker as we call them in Dorchester, in those neighborhoods. And I'll tell you, they're just stunned there. They're just absolutely stunned.

I talked to a priest at the church at St. Ann's, and tonight they're having a candlelight vigil. They moved it from the church to a neighborhood park. People were coming by all day long. Our Gary Tuchman was outside the family's home for most of the day. People coming by, dropping flowers off. Again, everyone is stunned. Three fatalities. None is more important than others. But when you have an 8-year-old, a young boy just standing there so close to the finish line. I can tell you, it is really, as I said, too close to home.

My younger brother sent me a message today, saying, "Loved Little League, loved Boston, with his parents. That could have been any one of us."

BLITZER: What a sad, sad story indeed. I don't know how these people can cope, can continue in heartbreak like that. Thanks very much.

That's it for me. Thanks very much for watching. "ERIN BURNETT OUTFRONT" starts right now.