WASHINGTON — The F.B.I. has concluded that there was little its agents could have done to prevent the Boston Marathon bombings, according to law enforcement officials, rejecting criticism that it could have better monitored one of the suspects before the attack.

That conclusion is based on several internal reviews that examined how the bureau handled a request from a Russian intelligence agency in 2011 to investigate whether one of the suspects, Tamerlan Tsarnaev, had been radicalized during his time in the United States.

Mr. Tsarnaev, who along with his brother, Dzhokhar, came to the United States about a decade ago from the Russian republic of Dagestan, was killed during a shootout with the police four days after he and his brother detonated two bombs at the finish line of the marathon, killing 3 people and injuring more than 200, the authorities say.

Members of Congress have contended that the F.B.I. should have done a more extensive investigation of Mr. Tsarnaev in response to the Russian request. And they have said the bureau should have followed up with Mr. Tsarnaev after he returned from a trip to Russia in 2012.