But an hour delay in the departure of the flight may have saved everybody on board, the source said.
A military grade of the explosive TNT caused the explosion on the Somali airliner, two other sources with knowledge of the investigation told CNN, citing an initial analysis of residue recovered from the aircraft.
Experts told CNN it was unlikely a forensic examination of the airplane would so quickly have provided clues about the sophistication of the device because the laptop was blown into many pieces. They said the most likely explanation for such a quick assessment was that investigators were able to look at a saved copy of the X-ray scan.
A Somali official told CNN that a piece of the keyboard from the laptop and the laptop bag, although burned, survived the explosion.
The airport worker wearing a white shirt in the surveillance footage died in mysterious circumstances three days after the attack when a vehicle he was in exploded, a Somali official close to the investigation told CNN. Just before the explosion, the person to whom the vehicle belonged -- the man in a yellow vest in the surveillance video -- had gotten out of the car so he could buy something at a shop. He was taken into custody, according to the official.
The same official backtracked from his earlier assertion that both airport workers were arrested.
Lax standards in security 'elephant in the room'
It was not clear what kind of X-ray machine failed to detect the explosive device nor whether the laptop was subject to other explosive detection systems. Most airports in the developed world use the latest generation of multiview X-ray machines, but some airports in less developed parts of the world still use single-view X-ray machines significantly less reliable in detecting explosives.
Many airports in Africa and across the developing world also lag behind in the deployment of explosive trace detection technology, or ETD. In a practice familiar to many air travelers, security staff take swabs that are placed into a machine and can detect minute quantities of explosive residue.
The latest generation of X-ray machines and ETD, when used in combination, are generally good at detecting TNT and should catch the explosive, even if it were concealed in the electronics of a laptop, because ETD swabs can detect minute amounts of residue, according to William McGann, an explosive detection expert at Implant Sciences, a U.S. company that manufactures explosive detection systems.
McGann told CNN that when modern multiview X-ray systems are used alone there is a chance the clutter in the X-ray image caused by the laptop could lead operators to overlook anomalies flagged by the technology. "Single view X-rays, on the other hand, would be totally reliant on a very vigilant screener at best -- and TNT concealed in a laptop could be easily missed," he added.
Lax standards in airport security across Africa and in many developing nations across the world has been the "elephant in the room for a long, long time," an explosives expert with experience in Somalia told CNN on condition of anonymity.
"When terrorists start changing their methods to the point where their explosive devices are no longer just a bag of bolts or a steel pipe, then the rest of the world needs to be worried. These sorts of disguised devices are disturbing. A perpetrator may not fool the world-trained expert looking at the device on an X-ray, but a half-bored official without the same training might let something slip by. They are starting to defeat visual technology. It's only as good as the operator," the expert said.
Robert Liscouski, a former senior official at the Department of Homeland Security and president of Implant Sciences, said there's an urgent need for better training of airport workers.
"In developing countries where there are significant challenges to training and maintaining an effective security workforce, it is almost impossible to have a security system that won't have process vulnerabilities," Liscouski said.
One avenue of inquiry for investigators will be whether the laptop received less scrutiny by staff manning the X-ray machine because airport workers brought it in.
Somali investigation called open
The Somali government has been open and cooperative with its international partners in the investigation so far, a Western official in Mogadishu said.
Jangali, the Somali transport minister, told CNN the investigation was progressing well.
"Hopefully when we conclude the investigation, we can share this information we have gathered with other intelligence agencies," he said by phone. "It's too early to speculate on the exact nature of this attack. We first want to find out exactly what happened, the sequence of events and all the people involved to get the complete picture."
Laptop used in earlier attack
If the Somali terrorist group Al-Shabaab
built the explosive device in the plane bombing, it would represent a significant elevation in its bomb-making capabilities, according to analysts. Given the sophistication of the device, one possibility is that al Qaeda affiliate in Yemen -- al Qaeda in the Arabian Peninsula -- shared technology with the group. AQAP bomb-maker Ibrahim al Asir
i has been developing a new generation of explosive devices concealed in electronics, according to Western intelligence officials, and there are indications the group has shared this technology with al Qaeda affiliates in Syria.
Last week's explosion in the air above Somalia wasn't the first case of a laptop bomb being used to try to target civilians in the Somali capital.
In November 2013, Al-Shabaab deployed a laptop bomb at the city's Hotel Maka.
A confidential source close to that investigation at the time provided photos of the device, saying they show that the bomb was faulty. The incomplete detonation, however, led people in the hotel to run outside the building, and when first responders arrived, a suicide bomber drove a car bomb into the group, killing six and injuring more than a dozen.
More than 40 arrests so far, official says
No group has claimed responsibility for the Daallo plane attack. U.S. officials said Al-Shabaab is the most likely culprit. The terror group attacked a restaurant and hotel last month on Mogadishu's Lido Beach, killing dozens of Somalis.
A Somali official close to the investigation told CNN that three field tests for explosives were conducted at the explosion site on the plane. All tested positive for explosive residue. Now those tests have been sent to labs in the United States.
According to the official, Borleh, the suspected bomber, was seated in 16 F on the plane. Investigators found parts of the laptop -- a piece of keypad -- and the laptop bag burned. The explosive device was hidden inside the laptop. The plane was at 12,000 feet when the explosion occurred. Borleh's right leg and right hand were blown off -- leading investigators to believe the bag was somewhere on his right side.
The source said Borleh's injuries were consistent with those suffered in an explosion, and he had explosive residue on him when his body was recovered. Borleh was heading to Turkey, ostensibly for medical reasons. He ended up taking the Daallo Airlines flight to Djibouti after a Turkish Airlines flight he had booked was canceled.
There have been 45 arrests made so far in the case, and those are some people who were directly and indirectly involved, the Somali official said.
Somalia's criminal intelligence division and explosive ordinance disposal team are leading the investigation. People are being interrogated, surveillance footage is being combed through from the 92 closed-circuit TV cameras at the airport, the official said.
"We have minute-by-minute footage of the event," the official told CNN.
New security standards at Mogadishu airport
Somalia has begun using new search and security methods at the Aden Adde International Airport in Mogadishu, including bomb-sniffing dogs, says Ali Ahmed Jama Jangali, the Somali transport minister.
Passengers said sniffer dogs were now searching their luggage at the airport. These dogs are not new; they are part of the Somalia National Police's explosive ordinance disposal teams.
Until now these canines and their Somali handlers have been deployed at big events or during VIP visits -- but Jangali said they would become a regular feature at the Mogadishu airport.