The incident occurred on June 22, 2016, when an off-duty Atlanta officer notified dispatch about a suspicious person at an apartment complex.
Former Officer James Burns responded and tried to block the path of a car, carrying victim Devaris Rogers, which was leaving the scene, the DA said.
"Despite the fact the Ford Fusion made no attempt to strike the officer and Burns was safely standing at the rear of his own patrol vehicle, Burns pulled his service weapon and fired one shot into the passenger side of Roger's vehicle," the statement said.
Rogers was struck in the head and his car continued down the street before crashing into a parked car.
"At the time of the shooting, Burns was not provided with any facts describing Rogers as a threat to the officer or the public. Neither was Rogers identified as the man the off-duty officer had previously reported," the DA's statement said.
Burns was fired on July 1.
He faces charges of felony murder, aggravated assault and violation of oath, the DA said.
A call to Burns' representative in his internal affairs review was not immediately returned.
Burns told investigators in an interview a week after the shooting that he "didn’t know to block that particular car," according to the Atlanta Journal-Constitution. “I shot at the car who was trying to run me over and kill me.”