Lawmakers are already criticizing the FBI for letting Tamerlan Tsarnaev slip away, and the revelation on Wednesday that the CIA had also investigated Tsarnaev and added him to terror watch lists will only increase questions about what more the agencies could have done. Senator Susan Collins said this week that she's “very concerned that there still seem to be serious problems with sharing information, including critical investigative information” — though it seems the bigger problem might be that there just wasn't enough evidence that Tsarnaev was becoming radicalized.
The New York Times reports that about six months after Russian intelligence contacted the FBI over it's concerns that Tsarnaev “had changed drastically since 2010," the Russians sent a nearly identical request to the CIA. Eventually both agencies cleared Tsarnaev, but he was added to the Terrorist Identities Datamart Environment, or TIDE, which contains about 700,000 names. The information sent to the watch list consisted of “two possible dates of birth, his name and a possible variant" — exactly what was sent by Russian intelligence — but the names were misspelled and the birth dates were incorrect. The FBI also added Tsarnaev to the Treasury Enforcement Communications System, which was set up to alert customs officials when Tsarnaev left the country, as he did when he went to Russia for seven months in 2012.
“The system pinged when he was leaving the United States,” Napolitano said at a Senate hearing this week. “By the time he returned, all investigations had been closed.” The Washington Post notes that since the CIA became involved later, it's possible Tsarnaev would have still been on the TIDE list when he reentered the country. "If Customs officials had alerted the FBI to his return, the bureau might have found reason to question him further in the months leading up to the attacks," the paper reports.
However, that seems fairly unlikely. The CIA and FBI asked the Russians for more information on Tsarnaev several times, but got no response until the manhunt was on in Boston. Therefore, he was just a man two agencies had cleared on a list of hundreds of thousands of potential terrorists. A U.S. intelligence official noted Tsarnaev “did not come anywhere close to being a selectee” for the no-fly list. As for what would have happened if the FBI was aware of his return from Russia, the official said, “Probably nothing.”