If you're confused about the byzantine web of watch lists designed to stop terrorists in their tracks, you're not alone.
Today, the FBI came under greater scrutiny with the revelation that suspected Boston Marathon bomber Tamerlan Tsarnaev was in fact on multiple government watch lists ahead of his deadly massacre in Boston last week. According to Reuters' ace investigative reporter Mark Hosenball, Tamerlan was placed on the government's highly classified Terrorist Identities Datamart Environment (TIDE) database and the declassified Terrorist Screening Database.
What does that mean, and how do these lists compare to more serious lists such as the "No Fly List" or the lethal "Disposition Matrix"? Above, we've fashioned a crude Venn diagram of the sprawling web of government watch lists. While up-to-date information about each list is notoriously difficult to obtain, this should give you a sense of where Tamerlan fit on the spectrum of suspected terrorists (the diagram is not set to scale).
Tamerlan was first placed on TIDE, a massive database controlled by the National Counterterrorism Center, after an FBI interview based on a tip from Russian authorities in 2011 that Tamerlan had become radicalized. The latest information about the size of TIDE's database is from 2008, when it contained more than 540,000 names representing about 450,000 real people (multiple spellings of names inflate the overall number).
Terrorist Screening Database
The next list Tamerlan found himself on, according to Hosenball, was the Terrorist Screening Database, a declassified version of TIDE with fewer details about individual suspects. According to the Washington Post, the Terrorist Screening Database contained more than 400,000 unique names as of 2009. Around the time Tamerlan was placed on this list, he was also placed on a list managed by the Homeland Security Department's Customs and Border Protection bureau, which flagged Tamerlan's visit to Russia in January 2012. Hosenball suspects that this didn't trigger an alarm because the "FBI had not identified him as a threat after the interview."
The Selectee List is significantly smaller than the previous two (14,000 names) and calls for mandatory secondary screening at airports. Tamerlan was not placed on this list, according to Hosenball.
No Fly List
Even smaller is the No Fly List, which, as of 2011, included about 10,000 people. According to NPR, the No Fly List is for passengers who authorities believe threaten the plane or could be "traveling somewhere to commit a terrorist act or went to a terrorist camp." No one is told whether they're on the No Fly List, so people don't typically find out until they arrive at the airport. By all accounts, Tamerlan was not on the No Fly List.
This is the list you really don't want to be on. No one knows exactly how large the Disposition Matrix is, but it's the second iteration of the White House kill list and it "spells out the intelligence on targets and various strategies, including contingencies, for handling them," according to reports. For some, "handling" includes a lethal drone strike. Tamerlan is not believed to have been on the matrix.