NEW YORK (VINnews) — An NYPD detective wounded during a confrontation with an armed teenager in Brooklyn may have been struck by friendly fire, according to law enforcement sources cited by the New York Post.

Detective Robert Karroll was shot in the back shortly after 4 a.m. Sunday while confronting an 18-year-old armed with a 9mm handgun in the Crown Heights neighborhood. Police have said Karroll’s bullet-resistant vest prevented more serious injuries.

According to the report, investigators believe the detective may have been hit by a round fired by another officer during the exchange of gunfire. Three of the four officers at the scene reportedly discharged their weapons, while investigators continue working to determine who fired the bullet that struck Karroll.

Authorities have said the suspect approached the officers’ unmarked vehicle before the shooting. The teen was arrested several blocks away and is expected to face charges. He was not injured during the incident.

A female officer sustained minor injuries during the confrontation.

Karroll, a veteran detective and father of three who was reportedly days away from retirement, was treated at a hospital and released later Sunday. Police have said he is expected to make a full recovery.

The New York Police Department has not publicly confirmed whether friendly fire was responsible for the detective’s injury, and the investigation remains ongoing.