WASHINGTON, April 23 (Reuters) - The name of one of the Boston Marathon bombing suspects, Tamerlan Tsarnaev, was listed on the U.S. government's highly classified central database of people it views as potential terrorists. But the list is so vast that this did not mean authorities automatically kept close tabs on him, sources close to the bombing investigation said on Tuesday.
Tsarnaev, 26, was killed in a police shootout early Friday, while his younger brother Dzhokhar, 19, was captured later that day. Prosecutors say the brothers, ethnic Chechens who had been living in the United States for more than a decade, planted two bombs that exploded near the finish line of the marathon on April 15, killing three people and wounding more than 200.
The sources said Tamerlan Tsarnaev's details were entered into TIDE, a database maintained by the National Counterterrorism Center, because the FBI spoke to him in 2011 while investigating a Russian tip-off that he had become a follower of radical Islamists.
The FBI found nothing to suggest he was an active threat, but all the same placed his name on the "Terrorist Identities Datamart Environment" list. The FBI has not said what it did find about Tsarnaev.
But the database, which holds more than half a million names, is only a repository of information on people who U.S. authorities see as known, suspected or potential terrorists from around the world.
Because of its huge size, U.S. investigators do not routinely monitor everyone registered there, said U.S. officials familiar with the database.
As of 2008, TIDE contained more than 540,000 names, although they represented about 450,000 actual people, because some of the entries are aliases or different name spellings for the same person. Fewer than 5 percent of the TIDE entries were U.S. citizens or legal residents, according to a description of the database on the NCTC website.
TIDE AND OTHER DATABASES
The TIDE database is one of many federal security databases set up after the Sept. 11, 2001, attacks. The database system has been criticized in the past for being too cumbersome, especially in light of an attempted attack on a plane in 2009. Intelligence and security agencies acknowledged in Congress that they had missed clues to the Detroit "underpants bomber" Umar Farouk Abdulmutallab. Officials said after the incident that he had been listed in the TIDE database.
Republican Senator Susan Collins said there were problems in sharing information ahead of the Boston bombings, too.
"This is troubling to me that this many years after the attacks on our country in 2001 that we still seem to have stovepipes that prevent information from being shared effectively," she said. Collins was speaking after the FBI gave a closed-door briefing to the Senate Intelligence Committee on Tuesday, but she did not elaborate.
However, in the case of Tamerlan Tsarnaev, the issue appeared to be that because he was not deemed an active threat, his name was only briefly on a list that would have triggered monitoring.
Tsarnaev was not put on the "no-fly" list that would have banned him from boarding an airplane in the United States. Neither was he named on the Selectee List, which would have required him to be given extra security screening at airports.
Another list, the Terrorist Screening Database, is a declassified version of the highly classified TIDE with fewer details about terrorist suspects. One source said Tsarnaev was on this list, too.
After being put in the TIDE system, his name was entered in another database, this one maintained by the Homeland Security Department's Customs and Border Protection bureau which is used to screen people crossing U.S. land borders and entering at airports or by sea.
Tsarnaev was flagged on that database when he left the United States for Russia in January 2012 but no alarm was raised, presumably because the FBI had not identified him as a threat after the interview.
When he returned from Russia six months later, he had already been automatically downgraded in the border database because there was no new information that required him to continue to get extra attention. So he did not get secondary inspection on his re-entry at New York's JFK Airport. It was unclear exactly what the procedure was for such a downgrade.
Sean Joyce, deputy director of the FBI, defended the FBI's performance in the Boston bombings at two closed hearings in Congress on Tuesday.
While government agencies declined to publicly discuss how the watch list system handled Tsarnaev, Homeland Security Secretary Janet Napolitano disclosed some details at a separate, open hearing on immigration on Capitol Hill.
"Yes, the system pinged when he was leaving the United States. By the time he returned, all investigations - the matter had been closed," Napolitano told the Senate Judiciary Committee on Tuesday.
Bob Grenier, former chief of the CIA's Counterterrorism Center, said the effectiveness of watch list systems is dependent on what information was put in them, adding that unless authorities had a strong piece of information against somebody, they were not going to put restrictions on people in a free society.
Republican Senator Lindsey Graham said law enforcement should have kept a closer eye on Tsarnaev after the FBI spoke to him two years ago. The FBI should also have realized last week following the bombings that he was in databases, Graham told reporters.
"After the bomb went off, don't you think one of the first things the FBI would do is say, 'Have we interviewed anybody in the Boston area that may fit the profile of doing this?' How could his name not pop up, the older brother? And when you have the photo the whole world is looking at, how could we not match that photo with him already being in the system?" Graham said.
(Reporting by Mark Hosenball; Additional reporting by Richard Cowan and Susan Cornwell; Editing by Alistair Bell, Frances Kerry and Eric Beech)