Terrorism Identification Datamark Environment (TIDE): This is a massive database that is maintained by the National Counterterrorism Center. As of December 2011, the database included more than 740,000 people, less than 2 percent of whom were US citizens or legal permanent residents. Names are removed when it is determined that they no longer meet criteria. In 2007, for example, nearly 23,700 names were removed. Tamerlan Tsarnaev was reportedly placed on this list after a tip from Russian authorities in 2011.
Terrorist Screening Database (TSDB): This is a separate database that is maintained by the FBI’s Terrorist Screening Center, and it’s mostly a subset of data from TIDE. As of May 2010, this database contained information on 423,000 people, about 5 percent of whom were US citizens and legal permanent residents. Tamerlan Tsarnaev was also reportedly placed on this list.
Selectee List: This list is much smaller than the other lists, with about 14,000 people included as of 2009, according to news reports. If someone is on here, they will be subject to mandatory screenings at airports. This list was originally run by the Transportation Security Administration, but now it is maintained by the FBI’s TerroristScreening Center. Tamerlan Tsarnaev was reportedly not placed on this list.
No Fly List: This list is for passengers that could be “traveling somewhere to commit a terrorist act or went to a terrorist camp.” The information is not public, and those who are on the list are not told if they are on it. An FBI spokesman told NPR in 2011 that about 10,000 people are on the list. This list was originally run by the Transportation Security Administration, but now it is maintained by the FBI’s Terrorist Screening Center. There are no indications that Tamerlan Tsarnaev was on this list.
Disposition Matrix : Developed by the Obama administration starting in 2010, this is said to be similar to the White House “kill list,” which tracks terrorists who are to be killed. It is not publicly known how many people are on this list, but there are no indications that it included Tamerlan Tsarnaev.
SOURCES: National Counterterrorism Center, FBI, news reports