A former Philadelphia officer was charged with murder in the fatal shooting of a 12-year-old boy in the back after the youth dropped a gun that he apparently fired at an unmarked police car, a prosecutor said on Monday.

Edsaul Mendoza, 26, who was dismissed from the force after the March 1 shooting, was charged with first-degree murder, third-degree murder, voluntary manslaughter and possession of an instrument of crime, according to a grand jury presentment unsealed on Monday. He was arrested on Sunday and denied bail on Monday.

A spokesperson for the Defender Association of Philadelphia, which represented Mendoza at his bail hearing, declined to comment on his case.

On the evening of the shooting, Mendoza was among four plainclothes officers involved in a stolen firearm investigation, riding in the unmarked car in South Philadelphia, District Attorney Larry Krasner said at a press conference.

Thomas “TJ” Siderio, 12, and another boy were riding bicycles when the undercover car drove past. A gunshot rang out, breaking the rear, passenger-side window of the undercover car, Krasner said.

“All indicators are that the 12-year-old fired the gun at the car,” Krasner said.