The Russian government declined to provide the F.B.I. with information about one of the Boston Marathon bombing suspects two years before the attack that would most likely have prompted more extensive scrutiny of the suspect, according to an inspector general’s review of how American intelligence and law enforcement agencies could have thwarted the bombing.
Russian officials had told the F.B.I. in 2011 that the suspect, Tamerlan Tsarnaev, “was a follower of radical Islam and a strong believer” and that Mr. Tsarnaev “had changed drastically since 2010 as he prepared to leave the United States for travel to the country’s region to join unspecified underground groups.”
But after an initial investigation by F.B.I. agents in Boston, the Russians declined several bureau requests for additional information they had about Mr. Tsarnaev.
At the time, American law enforcement officials believed that Mr. Tsarnaev posed a far greater threat to Russia.
The new inspector general’s report found that it was only after the bombing occurred last April that the Russians shared with the F.B.I. the additional intelligence, including information from a telephone conversation the Russian authorities had intercepted between Mr. Tsarnaev and his mother in which they discussed Islamic jihad.
“They found that the Russians did not provide all the information that they had on him back then, and based on everything that was available the F.B.I. did all that it could,” said a senior American official briefed on the review.
Mr. Tsarnaev, who was killed attempting to elude the police, and his brother, Dzhokhar, are believed to be the sole suspects in the attack, which killed three people and injured more than 200 near the marathon’s finish line. The Justice Department said in January that it would seek the death penalty against Dzhokhar Tsarnaev.
Federal authorities have uncovered little evidence tying the brothers to an international terrorist organization. F.B.I. agents who traveled to Dagestan, a region in Russia’s North Caucasus where Tamerlan Tsarnaev went in 2012 during a particularly violent period there, found nothing that showed he received training or encouragement from terrorists.
“At this point it looks like they were homegrown violent extremists,” the senior official said. “We certainly aren’t in a position to rule anything out, but at this point we haven’t found anything substantive that ties them to a terrorist group.”
The report was produced by the inspector general for the Office of Intelligence Community, which has responsibility for 17 separate agencies, and the inspectors general from the Department of Homeland Security, the Justice Department and the Central Intelligence Agency. It has not been made public, but members of Congress are scheduled to be briefed on it Thursday, and some of its findings are expected to be released before Tuesday, the first anniversary of the bombings.
Its contents were described by several senior American officials who spoke on the condition of anonymity because the report has not been publicly released.
The review is similar to an internal review the F.B.I. conducted after the bombing. In that review, the bureau found that its agents had been restrained from conducting a more extensive investigation because of federal laws and Justice Department guidelines that prevent them from using surveillance tools like wiretapping in investigations like those conducted on Mr. Tsarnaev before the bombings.
“Had they known what the Russians knew they probably would have been able to do more under our investigative guidelines, but would they have uncovered the plot? That’s very hard to say,” one senior official said.
While the review largely exonerates the F.B.I., it does say that agents in the Boston area who investigated the Russian intelligence in 2011 could have conducted a few more interviews when they first examined the information.
The report also recommends several steps it says the F.B.I. should take to more effectively share information with state and local authorities, the officials said. The F.B.I., which has worked with police chiefs from around the country over the past year on how it can better share information, has already adopted several of the recommendations, according to the officials.
When the F.B.I. disclosed shortly after the bombing that it had received information from the Russians, congressional Republicans and a few Democrats, including Representative William Keating of Massachusetts, criticized the bureau for not continuing to track him when he left to visit Dagestan and for not questioning him on his return in 2012.
“It’s people like this that you don’t want to let out of your sight, and this was a mistake,” said Senator Lindsey Graham, Republican of South Carolina. “I don’t know if our laws were inefficient or if the F.B.I. failed, but we’re at war with radical Islamists, and we need to up our game.”
As part of its investigation of Tamerlan Tsarnaev in 2011, F.B.I. agents examined his criminal and educational records and his Internet search history. They also interviewed him, his parents and people at his school. It was after those investigative efforts uncovered little that F.B.I. agents stationed in Moscow went back to the Russian authorities and requested any additional information they had on Mr. Tsarnaev, who immigrated to the United States from Dagestan a little more than a decade ago.
The exoneration of the F.B.I. stands in contrast to the findings of a similar investigation conducted after the 2009 shooting at Fort Hood, Tex., in which 13 people were killed. After the shooting, a former bureau director, William H. Webster, conducted a formal review of the investigation into the gunman, Nidal Malik Hasan, before and after the attack. That review said the F.B.I. had mishandled information garnered from intelligence, and it led to changes in the way the agency shares information.