Dzhokhar Tsarnaev, one of two brothers accused of bombing the Boston Marathon, told investigators that the pair had originally planned to mount an attack on the Fourth of July, a U.S. counter-terrorism official said Thursday.
Meanwhile, another counter-terrorism official said that Russian intelligence officials believe Tsarnaev's older brother, Tamerlan, may have met with militants while visiting Russia in 2012.
Authorities have scoured the background of the 26-year-old Tamerlan Tsarnaev for potential sources of radicalization in the years leading up to the bombings that left three people dead and more than 260 others wounded. They have focused on the six months last year he spent in Dagestan, a region in southern Russia.
Russian authorities had warned the FBI and CIA in 2011 that Tsarnaev might have ties to radical Islamist groups.
"It looks like there was some interaction," a counter-terrorism official said of the 2012 visit. "It doesn't seem like it was involving logistics or planning. They certainly weren't working with him because they were focused primarily on the traditional, Russian enemy."
The official, who requested anonymity because he was not authorized to speak about the investigation, added, "There is no evidence of pre-operational planning or training or even that this was a source of his radicalization."
The official who revealed the original target date of the Fourth of July also said that Russian intelligence had told U.S. officials that Tamerlan Tsarnaev met with an Islamic militant at a mosque in Dagestan last year. There is no evidence he got bomb training there, the official said.
By the time Tsarnaev arrived back in Boston in July, his views on Islam had grown more conservative.
He died after a gun battle with police in Watertown, Mass., on April 19. His brother was arrested that night.
Tsarnaev's body was released from the Office of the Chief Medical Examiner of Massachusetts in Boston on Thursday evening, spokesman Terrel Harris said. The body was claimed by an undisclosed funeral service on behalf of his family, Harris said, adding that burial information was considered private.
Dilanian reported from Washington and Pearce from Los Angeles.