Federal investigators are searching for "persons of interest" who might be linked to the April 15 bombings that killed three and injured more than 260 at the Boston Marathon, Reuters quoted a top U.S. lawmaker as saying on Sunday.
Authorities have in custody the younger of the two brothers suspected in the twin bombings, 19-year-old Dzokhar Tsarnaev. The other suspect, Tamerlan Tsarnaev, 26, died in an exchange of gunfire with police on April 18.
House intelligence committee Chairman Mike Rogers (R-Mich.) said on ABC's "This Week" that Tamerlan Tsarnaev had been "radicalized" during a 2012 trip to Russia.
"We still have persons of interest that we're working to find and identify and have conversations with," he added without specifying the number of such people.
"We are looking at phone calls before and after the bombing," panel Ranking Democrat C.A. Ruppersberger of Maryland told ABC.
The older brother reportedly discussed "jihad" during a 2011 phone conversation with his mother that was caught on a Russian wiretap. The family is of Chechen heritage, and the parents are now in Russia.
"I think they (Russia) have information that would be incredibly helpful and that they haven't provided yet," Rogers said.