NYPD detective shot in back confronting gun-toting teen was apparent victim of friendly fire: sources

Investigators believe that the veteran NYPD cop wounded during a chaotic confrontation with a gun-toting teen Sunday was struck by friendly fire, law-enforcement sources told The Post.

Detective Robert Karroll was hit in the back by a slug — and only saved from potentially deadly injuries by his bulletproof vest — around 4:15 a.m. when a deranged 18-year-old ran up on an unmarked police car in Crown Heights, authorities have said.

Karroll, a married dad of three who was just 10 days from retirement at the time, was in the vehicle along with three other officers — all of whom were in uniform, officials have said.

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Sources said the teen shooter  fired off his SAR 9 mm handgun, but it is unclear if he was aiming at the officers inside the black Kia SUV and whether he’s responsible for more than a half-dozen bullet holes in the vehicle, sources said.

Three of the four officers fired their weapons during the confrontation — which left the suspect unscathed and Karroll shot, sources said.

A female cop suffered minor injuries in the violence.

The unidentified gunman was nabbed several blocks away and is awaiting charges, sources said.

Karroll was released from the hospital hours later and  is expected to make a full recovery, police said.

Dramatic surveillance video footage obtained by The Post showed the gunman pacing back and forth on Nostrand Avenue with the weapon and racking a round in the chamber moments before he ran up on the unmarked vehicle.

The teen has no prior arrests in the Big Apple, but has at least one shoplifting charge in Essex County, NJ.