An East Pittsburgh police officer who shot and killed an unarmed 17-year-old running from a traffic stop Tuesday night was sworn in just hours before the fatal encounter.

Mayor Louis Payne told WPXI Wednesday that the unidentified officer who killed Antwon Michael Rose, of Rankin, previously spent seven years working in other departments, but confirmed that he was working his first shift following his official swearing in with the East Pittsburgh Police Department.

Allegheny County police officials said that Rose was a passenger in a vehicle stopped in East Pittsburgh around 8:20 p.m. Tuesday because it fit the description of a car seen fleeing the area of a shooting in the nearby borough of North Braddock. As an officer handcuffed the driver of the car, which investigators said had bullet damage to the back window, Rose and a second passenger got out of the car and ran.

Footage of the shooting posted on Facebook Tuesday shows the scene from a distance. The 18-second video shows Rose and the other passenger, who has not been found by police, get out of the car and make a break for the yard between two nearby houses.

Three shots are heard and one of the passengers appears to fall into the grass.

"Why are they shooting at him?" the woman recording the traffic stop says. "Why are they shooting? All they did was run and they're shooting at them!"

Rose, who police officials said was struck three times, was taken to McKeesport Hospital, where he was pronounced dead.

The Allegheny County medical examiner on Thursday ruled the teen’s death a homicide.

Though officers said they found two guns in the car after the shooting, Rose was not armed when he was shot, police officials said.

Click here to watch the footage of the shooting. Warning: Some viewers might find the images too graphic.

Pictured is the spot on East Pittsburgh's Grandview Avenue where unarmed teen Antwon Rose was shot and killed by a police officer Tuesday, June 19, 2018. Witnesses said Rose, 17, was shot in the back as he ran from a traffic stop.

Credit: AP Photo/Keith Srakocic

icon to expand image

Credit: AP Photo/Keith Srakocic

The officer who killed the teen has been placed on administrative leave while the Allegheny County police’s Homicide Unit investigates the shooting. Allegheny County District Attorney Stephen Zappala Jr. issued a statement Thursday in which he said he had met with police officials, but that the investigation into Rose’s death remained ongoing.

“Out of respect for the grieving process that the family and friends of Mr. Rose are going through and the upcoming Monday funeral for Mr. Rose, District Attorney Zappala will not have any further comment until next week.”

CBS News reported that the officers at the scene were not wearing body cameras. Their patrol cars also had no cameras. 

The shooting has sparked protests, including a protest of hundreds that shut down the street outside the Allegheny County Courthouse Thursday morning.  WPXI livestreamed the protest on Facebook.

Hundreds of people also gathered Wednesday night, despite rain pouring down on them.

Rose's family has hired civil rights attorney Lee Merritt, who talked to WPXI Thursday morning near the scene of the teen's death. Merritt said he was looking for witnesses to the shooting to determine what the officer might have seen as Rose and the other passenger fled.

Merritt told the news station that Rose’s family wants the officer to be treated the same as anyone who was shown, on video, shooting a man who was running away.

“If you take away the uniform and you put that same video out there, we believe that an arrest would have been made by now,” Merritt said. “Not necessarily a conviction, because that’s a process and everyone is entitled to due process.”

He said officers accused of misconduct should be treated like everyone else.

"It's very difficult to find justification for the use of deadly force given the facts as they were presented in that video," Merritt said. "Antwon and the other young man did not appear to present any harm or danger to that officer or anyone."

He said Rose’s family is devastated by his death.

"Every day that they wake up, they're hoping that this is all a bad dream," Merritt said.