A wiretap by the federal Drug Enforcement Administration to obtain evidence against a heroin trafficking ring uncovered a surprising suspect, officials said: a New York City police officer.

A heroin dealer, Guy Curtis, asked the officer on one occasion how to get “gunshot residue off your hands,” according to the authorities. And they said the officer, Devon Daniels, was once heard on the wiretap asking Mr. Curtis for help getting “any working revolver.”

Those requests and others were described in a criminal complaint against Officer Daniels that was unsealed on Tuesday in Federal District Court in Brooklyn. Shortly before, Officer Daniels, 30, was arrested on his way to work. The complaint accuses him of regularly misusing his authority to help Mr. Curtis, whom federal officials described as the head of a drug-dealing outfit in Queens known as Pov City.

Officer Daniels obtained a New York Police Department parking placard for Mr. Curtis, according to the criminal complaint, which was signed by Pathik R. Lotwala, an agent of the Drug Enforcement Administration.