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00:10 - Source: CNN

Story highlights

The Justice Department has launched an investigation into the death of Trayvon Martin

Florida governor's asks the state to assist probe as well

A neighborhood watch captain tells police he shot the teen in self-defense

The 17-year-old was not armed when he was killed last month in Florida

Sanford, Florida CNN  — 

A girl who overheard part of an incident involving Florida teenager Trayvon Martin can help prove he was killed “in cold blood” by George Zimmerman, a neighborhood watch volunteer, an attorney for Martin’s family said Tuesday.

The death drew protesters Monday to the courthouse in Seminole County, north of Orlando, to demand justice for Trayvon Martin, the 17-year-old who was shot and killed last month while walking back to his father’s fiancee’s house in Sanford.

Martin’s father said the family believes race was a factor in their son’s death, fueling public outcry over the incident in the racially mixed community 16 miles northeast of Orlando.

Late Monday, the Justice Department said it would dispatch officials to Sanford to investigate and “to address tension in the community.”

“The department will conduct a thorough and independent review of all of the evidence and take appropriate action at the conclusion of the investigation,” Justice Department spokeswoman Xochitl Hinojosa said in a written statement. “The department also is providing assistance to and cooperating with the state officials in their investigation into the incident.”

Florida Gov. Rick Scott also weighed in Monday evening, noting that the case has “caused significant concern within the Sanford community and the state” and asking the Florida Department of Law Enforcement to provide “any assistance necessary” to local investigators.

The man who shot Trayvon, George Zimmerman, has not been charged. He told police he shot the teen in self-defense, and police say they have no evidence to refute his story.

Trayvon’s father, Tracy Martin, told CNN’s “Anderson Cooper 360” that his son’s death was “a matter of profiling.”

“I think that’s an issue that Mr. Zimmerman himself considers as someone suspicious – a black kid with a hoodie on, jeans, tennis shoes,” Martin said. “Thousands of people wear that outfit every day, so what was so suspicious about Trayvon that Zimmerman felt as though he had to confront him?”

And the slain teen’s mother told NBC’s “Today” show that the neighborhood watch captain “was out there reacting to the color of his skin.”

“My son wasn’t doing anything but walking on the sidewalk, and I just don’t understand why this situation got out of control,” Sybrina Fulton said.

CNN has made numerous attempts to contact Zimmerman, who is Hispanic, but have been unsuccessful. In a statement to the Orlando Sentinel, his father says Zimmerman grew up in a multiracial family and has moved out of his home after receiving death threats.

And in announcing the federal probe, Hinojosa cautioned that bringing a civil rights case requires the government prove “that a person acted intentionally and with the specific intent to do something which the law forbids – the highest level of intent in criminal law.”

At the Seminole County courthouse, a handful of student protesters and a law professor from Florida A&M University met with a representative of the state attorney’s office to discuss the ongoing investigation while protesters demanded Zimmerman’s arrest. Many carried signs in remembrance of Trayvon.

“Gone but not forgotten,” read one that had a picture of the young man wearing a football uniform. “No justice for Trayvon. No peace for Sanford!” read another.

Assistant State Attorney Pat Whitaker told the students it would take several weeks to look at the case, but that the “investigation of the Sanford police needs to be greatly supplemented,” Jasmine Rand, the FAMU professor, said after the meeting.

The state attorney’s office also said a voice analysis would be conducted on 911 calls from the night of the shooting to determine who was yelling for help, students said.

Zimmerman, 28, called police around nightfall on February 26 to report a suspicious man in his neighborhood.

“Something’s wrong with him. Yep. He’s coming to check me out,” Zimmerman told a police dispatcher in a 911 call released Monday. “He’s got something in his hands. I don’t know what his deal is. Send officers over here.”

The teen started to run, Zimmerman reported. When he said he was following, the dispatcher told him, “We don’t need you to do that.”

Shortly afterward, neighbors began calling 911 to report a fight, then a gunshot. By the time police arrived, Trayvon lay dead. He was carrying a bag of Skittles and an iced tea that he had purchased at a nearby convenience store, and was headed back to his father’s fiancee’s home.

Martin said he’s “positive” that his son’s voice that can be heard screaming for help in the neighbors’ calls.

“It’s heartwrenching, because those actually were my son’s last words,” he said. “And to hear his last words being cries of help, is devastating. It tears me apart as a father.”

CNN’s Roland S. Martin, Rick Martin, John Couwels, Vivian Kuo and Terry Frieden contributed to this report.