Boston marathon bombing: Could it have been prevented?

The federal government added the name of the dead Boston Marathon bombing suspect to a terrorist database 18 months before the deadly explosions, U.S. officials told The Associated Press on Wednesday.

The CIA made the request to add Tamerlan Tsarnaev's name to the terrorist database after the Russian government contacted the agency with concerns that he had become a follower of radical Islam. About six months earlier, the FBI had separately investigated Tsarnaev, also at Russia's request, but the FBI found no ties to terrorism, officials said.

The new disclosure that Tsarnaev was included within a huge, classified database of known and suspected terrorists before the attacks was expected to drive congressional inquiries in coming weeks about whether the Obama administration adequately investigated tips from Russia that Tsarnaev had posed a security threat. Shortly after the bombings, U.S. officials said the intelligence community had no information about threats to the marathon before the April 15 explosions.

Tsarnaev died Friday in a police shootout hours before his younger brother, Dzhokhar, was discovered hiding in a boat in a suburban back yard.

The terrorist database is called TIDE, the Terrorist Identities Datamart Environment. Analysts at the U.S. National Counterterrorism Center submit names and even partial names into TIDE. About a year ago, there were some 745,000 people listed in the database. Intelligence analysts scour TIDE, trying to establish connections and update files as new intelligence is uncovered.

For entries with a full name, date of birth and intelligence indicating a reasonable suspicion that a person is a terrorist or has terror ties, the person's name is sent to a terror watch list, which feeds into lists like the one that bans known or suspected terrorists from traveling on planes.

Officials say they never found the type of derogatory information on Tsarnaev that would have elevated his profile among counterterrorism investigators and placed him on the terror watch list.

Five days after the U.S. determined who was allegedly behind the deadly Boston marathon terror attacks, Washington is piecing together what happened and whether there were any unconnected dots buried in U.S. government files that, if connected, could have prevented the bombings.

Lawmakers who were briefed by the FBI said they have more questions than answers about the investigation of Tsarnaev. U.S. officials were expected to brief the Senate on the investigation Thursday.

"The review is just beginning, but I haven't seen any red flags thus far," said Rep. Adam Schiff, a California Democrat who sits on the House Intelligence Committee and was briefed on the investigation Wednesday. House Judiciary Chairman Bob Goodlatte, R-Va., however, said lawmakers intend to pursue whether there was a breakdown in information-sharing.

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