Eric Ruch Jr., now 33 years old, was dismissed from the force in 2018, nearly a year after the shooting of 25-year-old Dennis Plowden.
Ruch turned himself in Friday morning. He had been with the Philadelphia Police Department for 10 years.
Ruch is charged with first-degree murder, third-degree murder, voluntary manslaughter and possession of an instrument of crime.
He is being held without bail.
District Attorney Larry Krasner released the findings from a grand jury presentment on Friday.
"According to the presentment, Eric Ruch killed Dennis Plowden while on duty by firing his gun directly at Plowden's head, as Plowden sat on the ground with his left, empty hand raised and clearly visible," Krasner said.
According to the grand jury, on the night of the December 2017 shooting, police in an unmarked vehicle made a radio call asking to run a tag on a white Hyundai. The tag was valid until the following year, police dispatch replied.
Plowden, who was driving the Hyundai, briefly pulled over but then took off, striking the door of a second unmarked police car. Why he fled is unclear.
Officers in those vehicles, along with officers in two marked police cars, pursued Plowden at a high rate of speed until he hit several parked cars, spun around, and crashed into a pole.
According to the grand jury, both of the airbags deployed and Plowden appeared to trip when he came out of the vehicle.
There was a "loud and chaotic scene," the grand jury said, and commands such as "don't move" and "show your hands" could be heard.
Within six to eight seconds of arriving on the crash scene, Ruch fired at Plowden, the grand jury said.
Krasner said the young father tried to obey the officers' commands. The grand jury said no weapon was found on Plowden or at the scene.
"It's indisputable that Plowden did not have a gun or any other weapon. It's indisputable," Krasner said.
According to a grand jury presentment, Plowden had his left hand raised. The bullet tore through several of Plowden's fingers before striking him in the head.
Plowden was pronounced dead the next day.
Several other officers on the scene took cover. Ruch was the only one who fired, the grand jury said.
In a statement issued Friday, Philadelphia Fraternal Order of Police Lodge #5 President John McNesby said the FOP will "represent former police officer Eric Ruch Jr. against these serious charges."
Plowden's widow, Tania Bond Plowden, has filed a civil lawsuit. She tells Action News the charges are just the beginning. She awaits a conviction.
"This is just one milestone, but we yet - still - haven't crossed that bridge. I'm very anxious and still on the edge of my seat," she said.
Civil Attorney Paul Hetznecker calls the charges the first step in a paradigm shift that holds police accountable.
"It's long overdue. There's been a long history of brutalization of the African-American community by the Philadelphia police," Hetznecker said.
Police Commissioner Danielle Outlaw did not elaborate on the charges. She says Ruch was fired under her predecessor, Richard Ross,and she will see how the case plays in court.