Nightly News   |  April 20, 2013

Investigators focused on Tsarnaevs’ background

While the crisis is over, the investigation of what motivated the suspects is just beginning. NBC's Michael Isikoff reports.

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>> the crisis is over, but the investigation of what motivated the suspects is just beginning. nbc's national investigative correspondent, michael isakoff, has spent the day looking into that.

>> investigators are intensely focused on the background of the tsarnaev brothers and what drove them to terrorism. meanwhile, federal prosecutors are prepared to file criminal terrorism charges that could carry the death penalty against the suspect. the younger suspect, dzhokhar tsarnaev, captured live last night, is under guard at a boston hospital. federal agents are waiting to question him. as soon as his medical condition allows, about whether he had any accomplices or any overseas connections. authorities believe his older brother, tamerlan , killed in a gun battle friday morning while wearing explosives strapped to his chest, may have instigated the plot. the brothers were raised in the u.s., living in the same house and seemed to fit in. both were athletic. dzhokhar, a wrestler, and tamerlan , a boxer. but in recent years, tamerlan changed.

>> there is someone who brainwashed him, some newly convert to islam.

>> in 2011 , the fear of chechnyan terrorism asked the fbi to investigate tamerlan based on investigation that he was a follower of islam according to an fbi statement. the fbi says a checked database interviewed tamerlan and family members, but quote did not find any terrorism activity, domestic or foreign. the fbi says it asked the russians for more, but never got answers.

>> without any strong derogatory information, the fbi would still be limited in what it could do.

>> in january 2012 , tamerlan flew to russia for six months. within a month of his return, tamerlan set up this youtube account, full of islamic jihadi postings. in this video, a radical prophesy.

>> no one can stop the jihad.

>> his parents say their sons were not terrorists and have been framed by the fbi . somebody clearly framed them. i don't know who exactly framed them, but they did. they framed them and they were so cowardly that they shot the boy dead. federal agents are determined to find out what motivated tamerlan and his brother, but they have tough questions for fbi officials about whether they could have done more to stop them. the justice department has decided to have the younger tsarnaev questioned for the first 48 hours by a special high valued interrogation team without advising him of his rights to council under what it calls a pushl safety exception, but senator john mccain and two others said that doesn't go far enough. they want tsarnaev treated as an enemy combatant under the laws of war.