Nightly News | April 20, 2013
>> the government's attempts to find out what motivated these summits, we're joined by andrea mitchell .
>> good evening. intelligence officials, the fbi , a global sernl really for what motivated tamerlan tsarnaev's terrorism. was it chechnyan nationalism, at the white house today, the president met again in the swaigs situation room with his national security advisers. he was briefed by the fbi director and others for 90 minutes . an official tells us afterwards that so far, there is no evidence of foreign involvement, but they're look. they say they are getting good cooperation now from russia , with whom the u.s. has had rocky relations. vladimir putin spoke with president obama last night and the two leaders are discussing the importance of working more closely together on counter terrorism in the future. the fbi said after interviewing tamerlan at russia 's request in 2011 , they sought and failed to get more information from russia 's intelligence and state security agencies, so a lot of questions still to answer. did these brothers join accept ratist factions? if so, why weren't they attack ing russian targets? this is a big mystery. tonight, the is commending his federal officials, also state and local officials, but they are still asking why did someone who was already in the fbi 's database get through the cracks. lester?