Over the past decade the New York City Police Department’s Intelligence Division (Intel) has built an active, fully staffed spying unit devoted to “mapping” the city’s large Muslim community in search of “home-grown” terrorists with no known ties to international jihadist groups. Their sense of alienation and resentment about the mistreatment of Muslims, it is feared, might lead them to commit “lone-wolf” attacks. Intel employs undercover informants, analysts, and spies, as well as “rakers” and “mosque crawlers,” in police parlance, who act as “human cameras,” and it opens investigations and files, without evidence of criminal activity, on unknown numbers of New Yorkers.1

Federal and local law enforcement agencies have revealed fourteen plots that have either failed or been foiled since September 11, 2001. It would be impossible to quantify the role the NYPD has played in this record. For example, the would-be Times Square bomber of May 2010, who reportedly had ties with the Taliban, was thwarted by a hot dog vendor who spotted smoke from a lit fuse in the parked SUV that held the terrorist’s bomb, and immediately reported it to nearby police.

The FBI has been responsible for aborting many of the plots, including a serious 2006 plan with international terrorist support, involving “martyrdom and explosives,” to destroy PATH train tunnels in order to flood the Financial District. And in 2006, a plot involving twenty-four suspects to use liquid explosives on commercial airliners bound for the US and Canada was thwarted by British law enforcement.

Certainly, the city’s regular police force of 36,000 officers, thousands of whom patrol the streets at any given hour, has been effective in protecting the public.2 But how much protection have the activities of the NYPD’s Intelligence Division itself provided? We do not know the intricacies of the relations between Intel and the rest of the NYPD; but Intel has initiated investigations and taken sole credit for arrests involving three separate potential attacks.

A common thread in all three cases has been the mental instability and subnormal intellectual capacities of the alleged terrorists. Each involved a sting operation and relied almost entirely on the testimony of a paid undercover informant. Mentally unstable people may be capable of great harm and paid informants may help detect serious crimes. But the facts in these cases warrant critical attention.

Jose Pimentel, a Dominican-American who converted to Islam, was arrested in November 2010 and charged with planning to use homemade bombs to attack US soldiers returning from Afghanistan and Iraq. Intel twice approached the FBI to become involved in the case—partnership with the FBI and, by extension, the US Attorney’s office helps ensure that a case…