(CNN) -- It's called the Terrorist Identities Datamart Environment, and weeks before authorities say he got on a plane with a bomb, Umar Farouk AbdulMutallab was in it.
The vast government databank, known as TIDE, is administered by the FBI's Terrorist Screening Center. It contains information about hundreds of thousands of people, the majority of them foreign nationals, who are suspected of having terrorist leanings.
An FBI official said AbdulMutallab was included in TIDE after his father warned the U.S. Embassy in Nigeria of his son's hard-line beliefs and possible ties to militant Islamists.
To understand how he could have been under the government's scrutiny and still make it onto a U.S.-bound plane with an explosive, you have to understand the way the government's watch list system works. TIDE is just the start.
The FBI uses the raw information contained in the TIDE databank to determine whether to put the subject onto the government's terror watch list, known as the Terrorism Screening Data Base. That list contains the names and aliases of about 400,000 people, but AbdulMutallab didn't make the cut.
According to Chad Kolton, a spokesman for the FBI's Terror Screening Center, there wasn't enough hard evidence to back up AbdulMutallab's father's fears, and so he wasn't placed on the terror list.
The bureau's own Web site spells out the criteria for inclusion in the screening database, saying that "only individuals who are known or reasonably suspected to be or have been engaged in conduct constituting, in preparation for, in aid of, or related to terrorism are included."
The determination not to put AbdulMutallab on the screening list had far-reaching consequences.
In May, the U.S. Justice Department's inspector general issued a report on the watch-list process, including a flow chart describing how anyone suspected of terrorist ties passes through a series of lists, the most serious of which includes the Transportation Security Administration's no-fly list. Making it from the TIDE database to the FBI's screening list is the key.
Because AbdulMutallab didn't make the screening database, his name could not then be sent onto the watch lists maintained by the TSA: the "selectee list," which law enforcement sources say includes about 14,000 names, and the "no-fly" list, which those sources say bans some 4,000 people from boarding any commercial flight destined for the United States.