Eric Ruch Jr.’s killing of Dennis Plowden, an unarmed Black man, after a high-speed chase was unjustified, a grand jury found.

A former Philadelphia police officer has been charged with first-degree murder in connection with the fatal shooting of an unarmed Black man after a high-speed chase in December 2017 that ended in a crash, prosecutors said Friday.

A grand jury concluded that the former officer, Eric Ruch Jr., was unjustified in shooting Dennis Plowden, 25, in the head, the Philadelphia district attorney, Larry Krasner, said in a statement on Friday.

According to information presented to the grand jury, Mr. Plowden, at the time of the shooting, “‘looked dazed and lost on the sidewalk’ having just stumbled from his car” after the crash, Mr. Krasner said in the statement. Mr. Ruch, who is white, fired directly at Mr. Plowden’s head “as Plowden sat on the ground with his left, empty hand raised and clearly visible.’”

It is indisputable that Plowden did not have a gun or any other weapon that night,” Mr. Krasner said at a Friday news conference.

Eric Ruch Jr., a former Philadelphia police officer, shot and killed Dennis Plowden after a high-speed chase in 2017, the authorities said.

In addition to first-degree murder, Mr. Ruch, 32, is also charged with third-degree murder, voluntary manslaughter and possession of an instrument of crime with intent. He turned himself in to the police on Friday morning, Mr. Krasner said at a news conference.

Mr. Ruch was denied bail, according to court records.

Paul Hetznecker, a lawyer representing Tania Bond, Mr. Plowden’s wife, said that Friday’s news represented a “bittersweet moment” for her “because she’s been waiting for the process of justice to begin.”

“It’s reminding her in a very public way of her tremendous loss,” he said.

Ms. Bond filed a federal lawsuit in September 2019 against Mr. Ruch and the city of Philadelphia in connection with her husband’s death. It alleges a conspiracy to commit an unlawful stop, excessive force and wrongful death.

Mr. Hetznecker said that he and the city were in negotiations.

The police union, Philadelphia Fraternal Order of Police Lodge 5, will defend Mr. Ruch, the order’s president, John McNesby, said in a statement on Friday.

“Our attorneys will review the allegations and appropriately defend this officer,” he said. “Officer Ruch Jr. is entitled to due process, and we believe the judicial system will protect his rights to a fair trial.”

The Police Department did not immediately respond to requests for comment on Friday.

The charges against Mr. Ruch came at a time when police brutality and killings by the police have received increased scrutiny following the deaths of George Floyd in Minneapolis and Breonna Taylor in Louisville, Ky. Mr. Krasner said he was aware of some distrust in his community between the public and law enforcement.

“We are trying to be fair,” Mr. Krasner said. “And trying to be fair means you are trying to be fair to marginalized people, you’re trying to be fair to powerful people, you’re trying to be fair to people that hold a position of public trust, and you’re trying to be fair to people who hold absolutely nothing in their hands.”

When asked by a reporter why it had taken nearly three years since the shooting for charges to be filed, Vincent Corrigan, an assistant district attorney, disputed that timeline. He said that the actual length of the investigation was about 12 months after accounting for logistical issues stemming from the grand jury procedure, as well as the coronavirus.

The chase on Dec. 27, 2017, began after Mr. Ruch made a radio call from an unmarked police car, asking to check the registration on a white Hyundai that Mr. Plowden was driving, according to prosecutors. After the police learned that the registration was valid, they said, Mr. Plowden, who pulled over briefly and then drove away, struck the open door of an unmarked police car.

That prompted the police to follow him “at high speed until he struck three parked cars, spun around, and finally stopped after striking a pole,” according to the district attorney’s office.

After the crash, Mr. Plowden got out of the car looking disoriented. Mr. Plowden’s left hand was raised over his face as Mr. Ruch fired his gun at Mr. Plowden, prosecutors said. The bullet passed through his hand and struck his head. No other officers present fired their weapons.

At the news conference on Friday, Mr. Corrigan, the assistant district attorney, said that despite previous claims the police had made about a white Hyundai being connected to a homicide case, it had not been definitely established that the police knew of any connection.

“There’s no information on the police radio before the incident that indicates that anyone knew for sure that this vehicle may have been involved in a homicide,” he said.

Nearly a year after the shooting, Mr. Ruch was dismissed from the Police Department.

Mr. Ruch used “poor tactics” when he shot Mr. Plowden, the police commissioner at the time, Richard Ross Jr., said at a 2018 news conference announcing the dismissal. Though Mr. Plowden was unarmed, Mr. Ross said that Mr. Ruch should have taken cover as the three other officers had, which would have “afforded him the opportunity to de-escalate the situation.”