A National Security official has confirmed the names of the Boston Marathon bombing suspects as brothers Dzokhar and Tamerlan Tsarnaev.
One of the brothers, Tamerlan, has been killed in a shootout with police overnight, while his 19-year-old brother is still at large.
The two men were legal permanent residents of the US, accordng to the NBC News agency.
The two suspects - identified to the Associated Press news agency as coming from a Russian region near Chechnya - killed an MIT police officer, injured a transit officer in a firefight and threw explosive devices at police during their getaway attempt in a long night of violence that left one of them dead and another still at large on Friday, authorities said.
A law enforcement intelligence bulletin obtained by the AP identified the surviving bomb suspect as Dzhokhar A Tsarnaev, 19, of Cambridge, Massachusetts.
Two law enforcement officials told AP that Tsarnaev and the other suspect, who was not immediately identified, have been living legally in the US for at least one year.
Russia's North Caucasus region has been plagued by an insurgency linked to separatist wars in Chechnya.