When a Russian intelligence service told the CIA that Tamerlan Tsarnaev had become an Islamic radical looking to join underground groups, the agency put his name in the government’s catch-all database for terrorism suspects.

The Terrorist Identities Datamart Environment list, known as TIDE, was the government’s attempt after the Sept. 11 attacks to consolidate a hodgepodge of watch lists, and ensure that every law enforcement agency would be alerted when it came into contact with a possible terrorist.

But TIDE has ballooned to 875,000 records, and critics say it is so all-encompassing that its value has been diminished. The database includes the names of young children of suspected terrorists and of people who have been cleared of suspected links to terrorism, officials say. A single credible tip raising “reasonable suspicion” is enough to add someone to the list.

TIDE is not a watch list — it is a highly classified intelligence database, a master list that feeds information at various secrecy levels to agencies that maintain their own watch lists.

Its biggest customer is the FBI, which runs the Terrorist Screening Database, also known as the consolidated watch list, which has hundreds of thousands of names. That database in turn feeds the “selectee list,” whose members are pulled aside for searches at airports, and the self-explanatory no-fly list of just a few thousand members. The FBI database also feeds the State Department’s watch list, which is designed to ensure that suspected terrorists don’t get U.S. visas.

Just being in TIDE or on the broad terrorism watch lists is not enough to justify special attention by law enforcement, officials say, and Tsarnaev, the Boston bombing suspect who was killed April 19 in a shootout with police, is a case in point. The database is so large and the records can be so vague that there often is little a law enforcement agency is willing or able to do in response to a TIDE match.

“To actually look at and get deeper into anybody on these lists, you have to get more information,” said Anthony D’Angelo, a former FBI agent who ran the Joint Terrorism Task Force in Chicago from 2004 to 2007.

“Would you buy a Ford?” an unnamed Department of Homeland Security intelligence officer was quoted as telling Senate investigators last fall in a Senate report that criticized TIDE. “Ford Motor Co. has a TIDE record.”

U.S. officials declined to address that claim on the record. They acknowledge that TIDE includes misinformation, but they say the database enables the kind of data sharing that officials wish took place in the months leading up to September 2001. As many as 60 CIA officers were aware of intelligence reports in 2000 that two al-Qaida figures who would become Sept. 11 hijackers, Nawaf al Hamzi and Khalid al Mihdhar, may have been in the United States — but no one notified the FBI.

“Is there information in TIDE which is inaccurate? Yeah, that’s why it’s called intelligence and not facts,” said Michael Leiter, former head of the National Counterterrorism Center. “But think about the idea that the CIA gets information that then is accessible to a cop on the street when he pulls somebody over. Nobody else in the world has anything remotely like that.”

The database includes terrorism financiers and supporters, and those believed to be casing potential targets, said a U.S. intelligence official who spoke on condition that he not be named. It includes multiple duplicate records, a second official said.

When Tsarnaev flew in January 2012 for a six-month trip to the Dagestan region of Russia, his entry in TIDE did not register with U.S. customs officials because two variants of his name and the date of birth typed into the system were incorrect, a U.S. intelligence official said. That wrong information was also transmitted to the FBI’s main terrorism watch list, the official said.

Tsarnaev had been interviewed by the FBI based on the same tip from the Russians, however, and his name had been entered correctly into yet another list used by customs officials to track the movements of persons of interest. That list includes about 22 million border crossing records, a counter-terrorism official said.

But since the FBI found no evidence that Tsarnaev was a threat, customs officials did not pull him aside for special questioning when he re-entered the country in July.

Tsarnaev returned to Cambridge, Mass., where authorities allege he and his younger brother, Dzhokhar, planned and carried out the Boston Marathon bombings.

Even if the TIDE entry on Tamerlan Tsarnaev had also popped up, the U.S. intelligence official said, “he’s not a selectee, he’s not been deemed a threat. I don’t know really if they would have given him a second look.”

A U.S. counter-terrorism official said Thursday that Russia’s intelligence service believes that while Tsarnaev was in Dagestan he met with militants.

“It looks like there was some interaction,” the official said. “It doesn’t seem like it was involving logistics or planning.” The militants were not working with Tsarnaev, the official added, “because they were focused primarily on the traditional, Russian enemy. There is no evidence of pre-operational planning or training or even that this was a source of his radicalization.”