A North Mankato police detective is charged with four felony counts for allegedly stealing prescription narcotics from a crime victim he had befriended.

Jeremy S. Swenson, 34, was charged Monday with three counts of fifth-degree drug possession and one count of theft, according to a criminal complaint filed in Nicollet County District Court.

“The allegations are basically that he had taken prescription medication — OxyContin — from a crime victim on several occasions,” said Special Prosecutor Jason Moran.

Moran, an assistant county attorney from Le Sueur County, is prosecuting the case to avoid a potential conflict of interest for prosecutors in Nicollet County where Swenson works.

The alleged victim, Gary Marti, met Swenson four years ago when he reported vandalism to his house, and Swenson interviewed him, Moran said. Marti told police that he had later given Swenson a number of OxyContin pills and a similar drug on separate occasions, then noticed a large quantity of his pills were missing.

Swenson told an agent for the state Bureau of Criminal Apprehension that he didn’t steal any pills. He said he was given the pills but conceded that he removed the pill-bottle label bearing Marti’s name, the complaint says.

Swenson told the agent that he was in an advanced pain management clinic for his increasing use of the drug. A pharmacist told authorities that Swenson had a prescription for OxyContin but was having his prescriptions filled so often that it appeared he was using more than the prescribed dosage.

Swenson has been placed on paid administrative leave until the case is resolved, said Police Chief Chris Boyer.

Boyer said he became aware on March 31 of the allegations, and that he and the city attorney decided to ask an outside agency, the BCA, to investigate.

Swenson is set for an initial court appearance on May 16.