Ever since 9/11, counterterrorism has been the FBI's No. 1 priority, consuming the lion's share of its budget—$3.3 billion, compared to $2.6 billion for organized crime—and much of the attention of field agents and a massive, nationwide network of informants.
After years of emphasizing informant recruiting as a key task for its agents, the bureau now maintains a roster of 15,000 spies—many of them tasked, as Hussain was, with infiltrating Muslim communities in the United States. In addition, for every informant officially listed in the bureau's records, there are as many as three unofficial ones, according to one former high-level FBI official, known in bureau parlance as "hip pockets."