By Joe Johns, Barbara Starr, Gloria Borger and Carol Cratty
Months after the FBI cleared Tamerlan Tsarnaev in its investigation of possible connections to jihadist causes, the Russians approached the CIA as well to look into him, CNN has learned.
But what was provided by the Russians in late September 2011 was "basically the same" information that had been given the previous March to the FBI, according to a government official.
The source said the communication was a "warning letter" sent to the CIA.
Tsarnaev, 26, suspected along with his younger brother of bombing the Boston Marathon early last week, died on Friday following a violent confrontation with police.
A law enforcement official said the CIA knew the FBI had done an assessment of the elder Tsarnaev, and the intelligence community seemed satisfied.
The FBI concluded its investigation in June 2011.
At the request of the CIA, information about Tsarnaev was included in the Terrorist Identities Datamart Environment list, otherwise known as TIDE, which is maintained by the National Counterterrorism Center, CNN has learned.
The list of more than 500,000 names of known or suspected foreign and domestic terrorists contains detailed, raw intelligence.
The Russians provided information that included "two possible dates of birth, his name and a possible name variant as well," the intelligence official added.
The amount of information the Russians provided is at the center of a critical look at whether the government missed signals of a man described as emerging jihadist who may have been further radicalized overseas.
"We just had a young person who went to Russia, Chechnya, who blew people up in Boston. So he didn't stay where he went, but he learned something where he went and he came back with a willingness to kill people," Secretary of State John Kerry observed on Tuesday.
The FBI investigated Tsarnaev based on the initial information from the Russians before concluding he was not a threat.
A senior U.S. official with direct knowledge of the information says "the issue with Russia is that the initial information was extremely thin."
The Russians believed he was "becoming radicalized."
"There were no details, no examples, no threads to pull," the source said. "Because of the rather light nature of the information we did go back to them and asked can you tell us more. We never heard back."
"They did not give a case report back when the United States inquired," said another source with knowledge of the investigation.
Officials have said that the FBI investigation went as far as it could based on the vague information.
"I think we did everything within our legal authority to vet this individual. When all was said and done there was nothing to link him to terrorism," a law enforcement official said.
What pinged the Russian interest?
The United States still doesn't know everything. But the senior U.S. official says the American intelligence community, including the FBI, is well aware the Russian security service monitors websites and online postings of particular militant websites.
"We know the Russians had to see something to make these claims," said the senior U.S. official.
The Russians have not told the United States whether they did any surveillance on Tamerlan while he was in Russia for six months in 2012, but the law enforcement official would not doubt the Russians kept tabs on Tsarneav.
If they did, according to the law enforcement official, the Russians never came back to the FBI and said so and didn't provide any additional incriminating information about him.
If the Russians held back information, it wouldn't be surprising, said a source familiar with the intelligence process and the flow of information.
The Russians are generally "more formal, more irregular" in providing this kind of information to us.
"'There's still a lot of suspicion" between U.S. and Russian intelligence operatives, the source said. "I am not sure they would share their source information with us."
The FBI is under very strict legal guidelines and standards when investigating Americans or persons on American soil. The standards are carefully scrutinized.