In the wake of Sept. 11, 2011, the New York Police Department has seen an unprecedented expansion of its surveillance and intelligence activities that includes actively spying on Muslim New Yorkers, The Associated Press reported.

The Federal Bureau of Investigation and local police officers were unaware of the domestic intelligence work, and escaped scrutiny from City Council officials in New York or the federal government, neither of whom received exact details. But one government agency took a large role in building up the NYPD's spying capabilities: the Central Intelligence Agency.

As The AP recounts it, a retired CIA veteran named David Cohen arrived at the NYPD a few months after Sept. 11, 2011 and recruited a former CIA colleague to assist him. They began dispatching officers to Pakistani neighborhoods and instructed officers to be more aggressive in searching homes and cars, but they ran up against a 20 year old court order requiring detailed evidence of criminal activity before the NYPD could monitor people. Cohen appealed to a judge and successfully had the guidelines relaxed.

Cohen began sending officers to observe and gather information in neighborhoods with large minority populations. Because officers were sent to neighborhoods whose minority populations shared the officers' own ethnic backgrounds, the espionage squad earned the informal moniker of the Demographic Unit. And because they were instructed to rake the coals, looking for hot spots, undercover officers became known as rakers.

Rakers would hang out at beauty stores, at cafes and at ethnic book stores -- anywhere where aspiring terrorists might purchase supplies, do research or plan potential attacks. Conversations they overheard -- for example, a shopkeeper expressing sympathy with Iraqi insurgents -- could mark an establishment as a hot spot that merited careful monitoring.

Other cities have rejected expanding their surveillance through similar tactics, The AP reported. Aspects of the NYPD's activities exceeded what even the FBI was legally permitted to do. Using undercover agents or deploying informants to a mosque without explicit reasons to suspect criminal activity would not be permissible under FBI rules.

If you're sending an informant into a mosque when there is no evidence of wrongdoing, that's a very high-risk thing to do, said Valerie Caproni, the FBI's general counsel. You're running right up against core constitutional rights. You're talking about freedom of religion.

But in New York, where 3,000 people perished in the deadliest attack on U.S. soil and plots continue to be foiled, the stakes are different.

The New York Police Department is doing everything it can to make sure there's not another 9/11 here and that more innocent New Yorkers are not killed by terrorists, NYPD spokesman Paul Browne told The AP. And we have nothing to apologize for in that regard.