>>> good evening. there is news tonight in the investigation of the boston bombings. newly discovered dna evidence on the bombs themselves. this comes as the investigation now stretches around the world and a big part of it is both the involvement of the russians and the cooperation between the russians and u.s. investigators who today, in addition to talking to anyone who might know something, were gathering new evidence to make this case. pete williams remains on the case for us and starts us off from our d.c. newsroom tonight. pete, good evening.

>> reporter: brian, good evening. legal sources say tonight that prosecutors and lawyers for the surviving bomb suspect, dzhokhar tsarnaev, have begun discussions about a possible deal in which he could avoid the death penalty in return for a full accounting to the fbi of what happened and why as investigators continue working to find those answers for themselves. in rhode island today an fbi team conducted a search at the home where tsarnaev's widow has been living since the bombing. she was shocked by the bombing and said she had no idea he was planning it. they took a sample of her dna to compare to dna on the bomb but they caution it could have come from employees at the stores where the parts were bought. u.s. officials confirm it was a russian wiretap of tamerlan tsarnaev's mother in which she spoke about jihad that prompted the russians to ask the fbi for more information about him two years ago. some members of congress say the russian intelligence service should have been more explicit.

>> if the russians had given the fbi the information they had regarding the mother and the son and their views on the mother's radicalization and the son's radicalization it would have dramatically changed the investigation.

>> reporter: tonight u.s. officials say they doubt it would have made a difference. they say it was clear two years ago the russians thought tsarnaev's mother was becoming an extremist but she spoke about jihad only generally. the fbi is looking at whether tamerlan tsarnaev met in dagestan with two men considered radical muslims. one was a boxer from canada. he was killed by russian special operations forces last july in dagestan. the other one, mahmoud nadal was killed last may. back home law enforcement officials say they found nothing landfills but are searching garbage containers in the belief someone may have carried items out of the dorm room days after the marathon bombings. authorities say it's not clear yet whether whoever may have done so knew evidence could be destroyed or did something just to help a friend. late today the judge in the case approved a request from joe car tsarnaev's lawyers to add a lawyer to his team. she represented jared loughner who pleaded guilty to the tucson shootings. brian?

>> pete williams starting us off from the d.c. newsroom tonight. thanks.