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One section of the Intelligence Division, the Terrorist Interdiction Unit, is devoted to using informers as "listening posts" in Muslim communities. The detectives in the unit cultivate the informers, place them in various communities, oversee their work and collect and compile the information that they generate.
Despite the Police Department's broad publicity campaign to highlight its counterterrorism efforts since 9/11, the unit has seldom if ever been mentioned in news accounts.
The police would provide no details about the unit and how it operates beyond what came out at the trial. So its scope, the guidelines under which it works and its successes and failures, beyond Mr. Siraj's conviction, could not be immediately determined.
But one paid informer alone — the man who testified against Mr. Siraj — attended 575 prayer services at the Bay Ridge mosque and another mosque in Staten Island over 13 months. He provided information almost daily, sometimes twice a day, to his detective handler, who prepared more than 350 reports based largely on the visits to the mosques and the Islamic bookstore.
Documents referring to numbered cases — M3 and M24 — that appear to be focused on mosques suggest that there could be as many as two dozen such investigations, but it could not be learned whether any others bore fruit.
http://www.nytimes.com/2006/05/28/nyregion/28tactics.html