WASHINGTON, District of Columbia (AFP) - The FBI said Friday it could not have done more to prevent the Boston Marathon bombings despite having been alerted to one of the suspects two years earlier.
"We came to that consensus at this point that there's nothing more we could have done under the existing guidelines, under the existing laws that govern our activities," an official from the federal law enforcement agency told AFP.
The April 15 twin blasts near the finish line, which killed three people and wounded more than 250, are believed to have been carried out by two brothers of Chechen origin, Dzhokhar and Tamerlan Tsarnaev.
Tamerlan, 26, died in a shootout with police several days after the attack.
Dzhokhar was arrested and faces a 30-count indictment - including 17 counts punishable by death. He has pleaded not guilty.
Russia alerted the FBI to Tamerlan in 2011, and the agency opened an assessment that included carrying out database checks and interviews with him and his family, the official said.
"The question was whether we did everything we could to pursue the information that was submitted to us by the Russians back in 2011," said the official, who requested anonymity.
"A lot of information was shared within the task force, we just believed we did everything we could," the official said, adding the FBI did not have the authority to carry out "more intrusive" searches and surveillance.
A controversy erupted following the blasts when it emerged that Russian intelligence had asked for Tamerlan, a legal permanent US resident, to be monitored because they felt he could be a threat.
Lawmakers and other high-profile personalities, such as the former New York mayor Rudy Giuliani, criticised the FBI for not having kept a closer eye on Tamerlan.
"If you've done everything you can legally to act upon the information you had and we were not able to find any derogatory information about Mr Tsarnaev... you couldn't charge him or arrest him, therefore he's able to go back to business as a resident of the US," the official said.
"I think it's fair to say we couldn't have prevented the attack. That's the feeling throughout the bureau," the official added.
"This notion that the attack couldn't have been prevented is consistent with all of our previous statements."