US security officials are to face questions in Congress over whether they mishandled information about the Boston Marathon bombing suspect Tamerlan Tsarnaev.
They will brief the Senate Intelligence Committee in a closed hearing on Tuesday after some Congress members accused the FBI of failing to act on Russian concerns.
Tsarnaev, 26, was questioned in 2011 amid claims that he had adopted radical Islam.
Three people were killed and at least 180 injured after two bombs exploded near the finish line of the marathon on 15 April.
Tamerlan Tsarnaev and his brother Dzhokhar were the subject of a manhunt following the bombings. Tamerlan, 26, was killed but his 19-year-old brother survived.
Federal prosecutors charged Dzhokhar Tsarnaev in hospital on Monday with using a weapon of mass destruction and malicious destruction of property resulting in death. He could face the death sentence.
Members of Congress want to know why no further action was taken after Tamerlan Tsarnaev was investigated in 2011 at the request of the Russian government.
Senator Dianne Feinstein, who chairs the intelligence committee, said that she and her colleagues would have to "sort it out" when they met FBI officials on Tuesday.
The BBC reports the full Senate is expected to receive a briefing later in the week.
Senator Lindsey Graham questioned why the FBI was unable to identify him as a threat based on his alleged links to radical websites.
He called for better co-operation with Russia and the amendment of privacy laws to allow closer scrutiny of suspects' internet activity.
Statement by widow's lawyers
Lawyers for Katherine Russell, 24, Tamerlan's widow, said that their client was doing everything she could to assist authorities.
She is "trying to come to terms with these events", her lawyers said in a statement on Tuesday.
"The report of involvement by her husband and brother-in-law came as an absolute shock to them all."
US delegation to interview parents
The United States embassy in Moscow says an American delegation has travelled to the Russian North Caucasus region of Dagestan to interview the parents of the Boston marathon bombing suspects.
The parents of Tamerlan and Dzhokhar Tsarnaev live in the overwhelmingly Muslim region on the Caspian Sea.
The Tsarnaev brothers had origins in the troubled, predominantly Muslim republic of Chechnya.
