Philadelphia District Attorney Larry Krasner announced Monday that a former city police officer who shot and killed a 12-year-old suspect after the adolescent reportedly fired at officers has been charged with murder.

Krasner says Thomas "T.J. Siderio" was unarmed at the time of the March 1 fatal shooting and that former officer Edsaul Mendoza knew the suspect was no longer a threat, the Washington Post reports.

Mendoza, 26, is charged with first-degree murder, third-degree murder, voluntary manslaughter and another charge for shooting Siderio.

Krasner said Mendoza and other officers were in an unmarked car that day when Siderio “likely” fired at the vehicle after officers stopped him and another boy for allegedly riding their bicycles the wrong way down a street.

Two of the officers, including Mendoza, returned fire and chased Siderio.

Mendoza was arrested Sunday, according to court documents.