New Developments in Boston Marathon Tragedy Reveal Bomb Design

FBI analysis of bombs used during marathon had toy car remotes as triggers.
3:00 | 04/27/13

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Transcript for New Developments in Boston Marathon Tragedy Reveal Bomb Design
We begin with breaking news tonight. Authorities here in washington following the fast moving developments in the case of the boston bombers. This evening a major new development. Abc news learned that russian authorities might have recorded a conversation between one of the bombers and their mother. A conversation that concerned authorities, they passed that information now to american investigators here. Abc gio benitez leus off boston tonight. Good evening. Reporter: Good evening, david. That wire tap conversation happening in 2011, the u.S. Just learning about it within the last week. It's just one of the many new details we're learning tonight. Investigators are zeroing in on tamarlan tsarnaev's movements before the boston bombing. What did he do during that six month trip to russia. A new government document obtained by abc news says the suspects must have used more than bomb making instructions found in al qaeda magazine. The fbi rebuilt the bomb and concluded the device was constructed differently. The most important aspect of the new documents is the russian link to tamarlan. In other words, did he receive training, of what type training. Of what individuals did he deal with. Reporter: Investigators wrapped up a three-day search of this new bed ford landfill for tamarlan's laptop. No word on what the fbi found in that search. Sources say agents found tamarlan's cell phone in a nearby apartment. Tonight questions remain about the role and whereabouts of a mysterious man who may have influenced tamarlan. His mother insisting misha was simply a friend. I'm sure that my kids were not involved. The suspect's mother we know was added along with her son tamarlan to a u.S. Terror watch list in 2011. She was called a religious militant. Back on boylston street stores and restaurants are buzzing with life. Atlantic fish steps away from the bomb site opening tonight for the first time since the attack. In a lot of ways it's like we're grand opening a new restaurant tonight. Absolutely. Reporter: You can see just how many people are here behind me on boylston street, many of them wearing these shirts and hats that say boston strong.

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

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