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."