Nightly News   |  April 17, 2013

To find suspect, ‘public has to be involved’

Discovering who was responsible for the bombings could take some time, but investigators are able to construct a mosaic using the many images provided, forensic evidence and secret intelligence, explains NBC National Security analyst and former Director of the National Counterterrorism Center Michael Leiter.

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This content comes from Closed Captioning that was broadcast along with this program.

>> former director of the national counterterrorism center . michael leiter is our nbc news counterterrorism analyst. you received from your sources a caution today that this perhaps was running on ahead of itself. and this can have a bad effect on an investigation.

>> absolutely. with all the media reporting about the possible arrests, they are very worried about the person or people being spooked and they are nervous about expectations at this point. for a while people were saying it's not going fast enough. now people expect an arrest in the near hours and the fact is knowing the person it can still take some time.

>> now about the evidence. we have a big maystack here. so far we have found some of the needles down to the zipper pull on what could have been the bag and the wires and the battery. we also have imagery -- tons of oh it -- and that has to be a big early help.

>> that is invaluable. it's something even three or four years ago we wouldn't have had. all of that imagery from the stores, the police and people, you combine that with the forensic evidence and the secret intelligence we are not hearing about from cell phone records, things like that. that paints the mosaic from which they find their suspect.

>> at logan airport in boston they were saying before you leave your city, do you have anything, do you remember anything? all of that helps.

>> absolutely. every bit of it. it does one more thing. it shows that the public has to be involved in this. it isn't just about saying fbi will go get them. people before an attack, after an attack, the public has a huge role e to play in helping them find someone and being resilient after.

>> the definition of social media . thank you.