WASHINGTON/CAMBRIDGE, Massachusetts (Reuters) - U.S. lawmakers demanded more answers on the Boston Marathon bombing on Wednesday, unsatisfied with the FBI reaction to warnings about one suspect and expressing doubt about the other suspect's claims that he and his dead brother acted alone.
Some on Capitol Hill questioned whether the Federal Bureau of Investigation and other U.S. security agencies failed to share information about suspect Tamerlan Tsarnaev in 2011, even after reforms enacted to prevent information-hoarding following the September 11 hijacked plane attacks 12 years ago.
Police say the ethnic Chechen brothers Tamerlan and Dzhokhar Tsarnaev planted and detonated two pressure-cooker bombs near the finish line of the marathon on April 15, killing three people and injuring 264.
Tamerlan, 26, was killed in a shootout with police and Dzhokhar, 19, was wounded, captured and charged with two crimes that could result in the death penalty if he were convicted. Dzhokhar remains in fair condition in hospital on Wednesday, U.S. officials said.
Attention has turned to whether U.S. security officials paid enough heed to Tamerlan Tsarnaev having been flagged as a possible Islamic militants by Russia. The FBI interviewed him in 2011 but did not find enough cause to continue investigating.
His name was listed on the U.S. government's highly classified central database of people it views as potential threats, sources close to the bombing investigation said. The list is vast, including about 500,000 people, preventing law enforcement from closely monitoring everyone on it.
Members of Congress were particularly concerned that U.S. Customs generated an alert when Tamerlan Tsarnaev left for Russia in 2012 but no one was aware when he returned and he was not re-interviewed.
"That's something that we have to look at," said Senator Dan Coats, a Republican from Indiana who is also on the Intelligence Committee. "That's one of the key things that we have learned and need to work on to make sure it doesn't happen again, and that is simultaneous communication to all the relevant agencies when a warning is posted."
Members of Congress briefed by law enforcement and media reports citing unidentified sources indicate Dzhokhar Tsarnaev has told investigators from his hospital bed that the brothers grew radical from anti-U.S. material on the internet and acted without assistance from any foreign or domestic militant groups.
"That basically seems to be the story, but I don't see how we can accept that," Representative Peter King, a New York Republican on House Homeland Security Committee, told CNN.
"It may end up being the truth but ... I don't see why he would be giving up any accomplices he may have or talking about any connections his brother may have had in Chechnya or Russia," King said on Wednesday.
Intelligence officials were scheduled to brief members of the House Intelligence committee about the Boston investigation behind closed doors later on Wednesday, and the full Senate was scheduled to receive its own briefing on Thursday.
Investigators have focused on a trip to Dagestan last year by the older Tsarnaev and whether he became involved with or was influenced by Chechen separatists or Islamic militants there.
In Grozny, the capital of Russia's volatile Chechnya region, a member of the extended family Tsarnaev said the brothers were victims of a Russian plot to portray them as Chechen terrorists operating on U.S. soil.
Among the remaining mysteries was how the bombers acquired the black powder used as explosives in the home-made pressure cooker bombs packed with nails and ball bearings. Tamerlan bought two large packages of fireworks in February from a store in Seabrook, New Hampshire, but the explosive powder they contained would not have been "anywhere near enough" to build the bombs, said William Weimer, vice president at Phantom Fireworks.
U.S. Vice President Joe Biden and law enforcement agents from around the United States attended a memorial in Cambridge, Massachusetts on Wednesday for a university police officer who authorities say was shot dead by the Tsarnaev brothers on Thursday night.
The service at the Massachusetts Institute of Technology honored Sean Collier, 26, with Biden praising a crowd of hundreds of uniformed and plainclothes police officers for their dedication.
"I'm standing for you. You should not be standing for me," Biden told the crowd as he took the podium. Addressing the slain officer's family, he said, "there is not much that I'm going to be able to do to fill that void, that sense of loss and grief, or answer those nagging questions of why."
Collier was killed about five hours after the FBI released pictures of the two suspects, asking for the public's help in tracking them down.
Police said the two then carjacked a vehicle and later engaged in a gunbattle with police in which Tamerlan was killed and Dzhokhar escaped. He was caught in the Boston suburb of Watertown on Friday night, hiding and bleeding in a boat, after a manhunt involving helicopters and armed vehicles that shut down the greater Boston area.
Additional reporting by Mark Hosenball; Writing by Daniel Trotta; Editing by Grant McCool