Quoted:
NYCPD has, or at least used to have, street crime units which were patrol officers (not detectives) in plainclothes. This just made it easier to move around unobserved. They would respond to various calls, as needed.
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NYPD had and currently continues to have several plainclothes units. These include:
SNEU (Street Crime Enforcement unit)
Anti-Crime ( Precinct based units staffed by PO's not Det's)
Intelligence
OCCB (Organized Crime Control Bureau)
Gang Unit (another precinct based unit staffed with PO's)
And I am sure there are a few more that I am unaware of and I think that SNEU may have a new name...but it is the same unit. Waverunnre would be more up-to-date about this than I would.