U.S. investigators have questioned the parents of the two Boston Marathon bombing suspects in the Russian republic of Dagestan, as they try to determine what might have influenced their sons in the months before the April 15 attack.
The American authorities, working with Russian security forces, interviewed both parents Tuesday night and called back the suspects' mother, Zubeidat Tsarnaev, for more questioning on Wednesday.
The investigators are particularly interested in any contacts the elder brother, Tamerlan Tsarnaev, might have had with Islamic extremists during a six-month visit to Dagestan and Chechnya last year.
U.S. lawmakers discussed the same trip Tuesday as they raised concerns about the sharing of intelligence among federal law enforcement agencies. Senator Lindsey Graham said the FBI told him it was not aware at the time of Tamerlan Tsarnaev's trip to Russia.
Tamerlan Tsarnaev died after a shootout with police last Thursday, while his younger brother Dzhokhar was captured a day later.
Meanwhile, in Boston, authorities on Wednesday reopened Boylston Street, the city thoroughfare where the explosions occurred near the finish line of the race.
Later, several thousand people gathered at the Massachusetts Institute of Technology for a memorial service for campus policeman Sean Collier, who authorities say the Tsarnaev brothers shot to death three days after the bombings.
Homeland Security chief Janet Napolitano told the Senate Intelligence Committee that her agency did know about Tamerlan's trip, but that an FBI alert on him had expired by the time he returned.
The FBI had interviewed Tsarnaev in 2011 at Russia's request, but found nothing to connect him to terrorism at that time.
The 19-year-old Dzhokhar has been charged with using a weapon of mass destruction. He is in federal custody in a Boston hospital.
U.S. officials say Dzhokhar told them in preliminary interviews that he and his brother were partly motivated by the U.S. wars in Iraq and Afghanistan, but that they were self-radicalized and not connected to any terrorist network. The two suspects are Chechens who came to the United States as boys.
The brothers allegedly set off two bombs alongside the Boston Marathon course, killing three people and injuring 264. At least 14 of the wounded lost legs in the blasts.