Eduardo Cornejo had been an officer in the New York Police Department for more than a decade. But in a phone call one night last month, the authorities said, he hinted at his other, more nefarious work.

“That might make it hot, though, standing outside with a bunch of girls,” Mr. Cornejo said, a reference, according to the authorities, to dividing money among the prostitutes he is accused of employing outside a Long Island motel. “They’re going to know what’s up real quick.”

But investigators were already aware of the operation, the authorities said on Tuesday. They were listening to the phone call — his line had been wiretapped — and had been tracking his movements for months after an anonymous tipster said Mr. Cornejo was a pimp for at least one woman.

In all, the authorities said, he had employed at least 10 prostitutes. Investigators followed him to motels across the region, and the authorities described his efforts as something of a second job, starting many evenings as soon as his shift ended with the Police Department.