Boston Marathon 2013: Explaining the Explosions

Former NYPD bomb squad Det. Kevin Barry says the bombs in Boston "didn't function fully."
3:22 | 04/16/13

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Transcript for Boston Marathon 2013: Explaining the Explosions
Welcome back as investigators begin to piece together the details of the attack at the Boston Marathon. They're asking the public to share their videos and pictures of the scene. Those images even the smallest details of those pictures will help pieced together this crime. And joining us now to talk more about this is former detective with the NYPD bomb squad can -- Commending you for joining us this morning we really do appreciate it. And our first question is what my investigators learn from the device that they discover that what I'm exploded we want to get to this question quickly because we have. Very interesting picture to show everyone. Most updated information I have is that what they thought was recovered device was not which -- state knapsack containing their property. Kevin let's move on -- looking at photographs. Investigators that didn't specialize suits combing through the scene you've taken extensive look at these pictures. And your expertise here on some of these bring to light what you you may see going on in these pictures. Investigators -- Suits that are under way is a Kevlar they weigh about a hundred yards east. And they are searching for remnants of the device. With the idea that this still may be light explosives in the area that's where they're throwing -- -- -- if you note to you'll also see an object blue in the center of the picture. That blue object is sitting in the seat of the explosion. It was not there at the time an explosion may have been pulled in to that whole. By a negative blast wave after the original explosive wave one outward. There's a negative -- -- Apple's. Objects back into the scene of the seat in the explosive. Kevin what is it that there and and we also see a very dark mark that seems to be on the sidewalk -- -- why is that significant and why would investigators be looking and that mark on the sidewalk. That's a thermal burn mark. Caused by the thermal -- -- -- -- in the explosive video followed by the smoke cloud going upward but white smoke. But on the ground -- source Ian -- -- windows. About twenty feet across and two feet from the building line -- towards occur. A white substance. Yeah we -- talk about it -- -- and we look that much in your opinion. My opinion is that that may be unexploded. Tertiary explosive either urea nitrate similar to used in the 93 -- -- World Trade Center. Or it may be ammonium nitrate. Commercially manufactured explosives. But those explosives needing who stirred to step up to speed of the work effect of the explosive to make it function. It appears. From what I can see there's a possibility that this bomb was bigger. And actually. We thought at first but it failed to function as designed it didn't have enough energy to completely. -- is a work effect in total destruction of the only explosive product so it didn't function fully. Well thank goodness and that is actually in fact the case. Mr. Barry want to thank you for your expertise we appreciate you joining us this morning. -- -- -- -- --

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

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