An innocent bystander was killed in an illegal gun investigation gone horribly awry in Westchester on Friday, after an NYPD officer opened fire in response to a gun being pulled on him.

According to police, an undercover NYPD officer was contacted by a suspected gun dealer, 28-year-old Jeffrey Aristy, who had apparently long been the subject of an NYPD investigation. After first meeting Aristy in the Bronx, the two drove to Mount Vernon to meet up with a second suspect, identified only as a 37-year-old man.

Upon arrival, the second suspect climbed into the back seat of the officer's car, put a gun to his head and demanded money. The officer complied, and as the suspect began to flee, the officer signaled his backup team. He attempted to stop the suspect, who pointed his gun at the officer again. This time, the officer opened fire, hitting the robber three times in the torso, but also inadvertently hitting 61-year-old Felix Kumi, who was standing nearby.

Both Kumi and the injured suspect were taken to Jacobi Hospital, where Kumi was pronounced dead. The officer was uninjured. An investigation uncovered, along with the officer's buy money, a replica .45 caliber gun.

Aristy has been charged with four counts of criminal sale of a controlled substance and two counts of criminal sale of firearms. Charges against the second suspect are still pending.