The New York Times reports
Russia declined to provide U.S. investigators information about Boston Marathon bombing suspect Tamerlan Tsarnaev two years before the deadly attack.
The newspaper said that according to an intelligence inspector general's report, Russian officials told the FBI in 2011 that Tsarnaev was a follower and strong believer in radical Islam.
It said Russia turned down the FBI's request for more details.
Top U.S. officials who have seen the report said the FBI did all it could with the information it had to follow up on Tsarnaev. But they could not say whether agents could have prevented the bombing.
Tsarnaev and his brother Dzhokhar came to the United States from Chechnya. They allegedly set off two bombs near the finish line of the Boston Marathon one year ago, killing three and wounding more than 260.
Tamerlan Tsarnaev was killed in a shootout with police. Dzhokhar was captured days later and is in federal prison awaiting trial.