(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." 
what did his father suspect he had ties with?
son's hard-line beliefs and possible ties to militant Islamists