Boston Marathon Bombing: The Manhunt

Authorities say they have a clear picture of a potential suspect in the bombings
3:00 | 04/16/13

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Transcript for Boston Marathon Bombing: The Manhunt
It's been two days since the deadly bombings at the Boston Marathon here and in that time the investigation. Into who. Was responsible for that atrocity has really accelerated with some very promising -- they found pieces. Of the bombs themselves fashioned from common pressure cookers their security camera. Footage from buildings around the city as there aren't so many cities and there are those thousands of pictures and videos taken by. Ordinary. Fans and supporters of the runners documenting every stage of that race. And now tonight as the FBI investigation continues and they are following every lead there is growing optimism. That they are closing in on the killer here's ABC's chief investigative correspondent Brian wrong. The federal courthouse in Boston. -- suspect would likely stand trial was evacuated late in the day because of a bomb threat that understandably was taken very seriously. When -- telling him. Yeah actually could call -- -- evacuate the building and no bomb was found. It was only two days ago that terror and tragedy struck -- at the finish line. That story patriot staying there. It set off a frantic search to find the killer or killers. -- an entirely new set of methods at the disposal of investigators. Are now looking for the person or persons responsible. Everyone does have a digital profile that offers you a couple of opportunities the first opportunity offers you. Is to try to find the right people to look at if someone's talking about an act of violence. That's somebody obviously he should come into the investigative lands. Authorities say the FBI has focused on photographs. Including some taken by a surveillance camera at the Lord & Taylor store that show a man in the race day crowd using a cell phone. -- black bag strapped across his chest that authorities say may contained the bomb. If in fact the FBI has -- face from surveillance video. The lord and Taylor's -- may be able to use facial recognition software. Do wrong not face against databases. The key frames are just a few of the millions of frames of video examined in the last 36 hours by a special team FBI forensic experts. They work for the operational technology division. They've set up facilities -- a restricted location near the Boston Harbor. This is where the evidence in the video is brought the agents are masters at using that facial recognition software. The new science of converting a face into a day. Demonstrated hereby grant Fredericks who runs an Indiana company that was used by the FBI following the 9/11 attacks. When he authorities will go for my face to a name is by getting the public's help. -- likely be -- the -- will be at such a distance that trying to do some kind of facial mapping or some electronic process and identify this -- cannot be effective. The Internet has been full of amateurs trying to do with themselves claiming that maybe they found the bombers. And Frederick says that has a huge downside. There's a danger. In the public playing junior G men and identifying. Potential suspects and putting them on the news. You don't know how that's -- effectiveness of person. And so it's a very dangerous. Game to play. In addition to the videos and photos the FBI tech agents are also examining tiny bits of debris recovered at the crime scene. There are -- wire fragments with the manufacturer's name. Tiny -- apparently used as shrapnel as well as the mangled remains of that pressure cooker that agents say was used to build the bomb. It may well have fingerprints still on it. They're going to be able to identify those items right down to perhaps the type of bag. The type of accelerant the type of detonator. All that becomes extremely important in a trial. If you can match those items to a particular suspect. Ultimately whoever is arrested for the bombing will almost certainly face at least three counts of premeditated murder. For the deaths of eight year old -- Richard. 29 year old crystal Campbell and a third victim identified only Wednesday Boston university graduate student Lindsey -- a native of China.

This transcript has been automatically generated and may not be 100% accurate.

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