U.S. lawmakers say federal investigators probing the Boston Marathon bombings are pursuing "persons of interest" in the United States who may have links to the attacks.
Speaking Sunday on ABC television, House Intelligence Committee chair Mike Rogers did not provide details. But he said better cooperation is needed with Russia to probe the movements of two suspects with ties to the southern Russian republics of Chechnya and Dagestan.
New details have emerged with reports that now-deceased suspect Tamerlan Tsarnaev spoke to his mother about jihad in a 2011 telephone call to the region that was secretly recorded by Russian authorities. CBS News reported that U.S. investigators only learned about the telephone call in the past several days.
Elsewhere Sunday, House Homeland Security Committee chair Michael McCaul said he believes Tamerlan Tsarnaev and his suspect brother, Dzhokhar, got training in explosives, considering the "level of sophistication" of the bombs that ripped through crowds viewing the April 15 marathon. McCaul spoke on "Fox News Sunday."
Investigators say 26-year-old Tamerlan and 19-year-old Dzhokhar planted two bombs near the finish line of the race, killing three spectators and wounding more than 260 others. Tamerlan was later killed in a shootout with police, and Dzhokar -- captured last week -- has been charged with using a weapon of mass destruction.
U.S. investigators have since questioned the suspects' parents in Dagestan to determine if Tamerlan had contact with Islamic extremists during a 2012 visit. Tamerlan was placed on a U.S. terrorism alert list in late 2011, after Russian authorities contacted the CIA with concerns that he may have become a radical.