NEWARK, N.J. — Americans living and working in New Jersey’s largest city were subjected to surveillance as part of the New York Police Department’s effort to build databases of where Muslims work, shop and pray. The operation in Newark was so secretive even the city’s mayor says he was kept in the dark.

For months in mid-2007, plainclothes officers from the NYPD’s Demographics Units fanned out across Newark, taking pictures and eavesdropping on conversations inside businesses owned or frequented by Muslims.