TODAY | April 21, 2013
>>> the investigation into the boston marathon bombings. we're getting a new look at the final moments before the suspected bomber dzhokhar tsarnaev was captured. infrared video from the helicopter shows him moving inside the boat a few moments later an exploeks from a flash bang grenade that goes off before agents moved in and took him into custody. federal charges could be filed against him as soon as today. our national investigative correspondent michael isikoff is in boston with the latest. michael, good morning.
>> good morning, lester. we could be?k? learning a lot more about the boston marathon bombing when federal prosecutors file those criminal charges , possibly as early as this morning, laying out some of the government's evidence against the surviving 19-year-old suspect. but, meanwhile, questions are mounting about how much the fbi knew before the bombing about his older brother and alleged accomplice and whether bureau officials failed to connect the dots. 19-year-old dzhokhar tsarnaev is being treated at a boston hospital today still not well enough to be grilled by federal agents about the bombings and shootings that terrorized the city.
>> serious but stable.
>> reporter: authorities believe that his older brother tamerlan killed in a gun battle early friday morning while wearing explosives strapped to his chest may have instigated the plot and persuaded dzhokhar to join him in the bloody attacks.
>> i am extremely lucky that i'm not at a funeral this morning for one of my officers.
>> reporter: but agents are puzzled by what motivated the tsarnaevs. they were raised in the u.s., lived in the same house and seemed to pit in. they attended this cambridge mosque but a spokeswoman says they raised no red flags .
>> in their visits, they never exhibited any violent behavior, sentiments otherwise they would have been immediately reported to the fbi .
>> reporter: but should the fbi have been watching more closely? in 2011 , russian intelligence concerned about the threat of chechnyan terrorism asked the fbi to investigate tamerlan based on information he was a follower of radical islam according to an fbi statement. the fbi said it checked databases, interviewed tamerlan and family members but, quote, did not find any terrorism activity, domestic or foreign. in january 2012 , tamerlan flew to russia for six months and visited chechnya. within a month of his return in august 2012 , tamerlan set up this youtube account full of islamic postings. in this video, a radical prophecy.
>> no one could stop that jihad. no one can stop it.
>> reporter: in a letter to obama administration officials, two top republican members of congress questioned why tamerlan remained at liberty in this country to commit the boston attack. and whether the bureau could have done more to watch them.
>> we can't be politically correct. we have to say, has radicalization extended into the chechen community?
>> reporter: the fbi says there was little they could do to legally monitor tamerlan tsarnaev once they -- initially determined he was not a threat. but one question congressional investigators have is, having gotten that initial tip from russian intelligence why didn't anybody at the bureau notice those radical youtube postings on the internet? lester?
>> we're going to get into that right now, michael isikoff .