Protesters took to the streets for the third straight day in Pittsburgh as anger mounted after a 17-year-old was fatally shot by the police while running away from an officer on foot.

County officials told The Washington Post that protests were expected in multiple locations around town. Early in the evening, a large crowd marched across the Roberto Clemente Bridge, which spans across Allegheny River from Pittsburgh's downtown toward its baseball stadium to protest Antwon Rose Jr.'s killing and then back again toward downtown, stopping in a square where they conducted a moment of silence and listened to speakers.

"We do this for Antwon!" they shouted.

Later, they linked arms as they planned to march on to the highway. The night before, another group of protesters had shut down an interstate in town for hours before riot police dispersed the crowd in the early morning. Other protests and vigils were expected around the country over the weekend.

Rose was killed on Tuesday night after being shot by a police officer who was investigating a drive-by shooting in which a 22-year-old man was injured when a shooter fired nine .40-caliber rounds at him from a car. The vehicle that Rose traveling in matched a witness description of the vehicle, police said, and it was pulled over about 15 minutes later.

Graphic video shows two men fleeing the car after it was stopped, with one of them falling to the ground after shots ring out. Police said that Rose was struck by all three bullets fired by the officer, whom officials identified as Michael Rosfeld, but have declined to say if Rose was shot in the back.

The Allegheny County Police Department is investigating the two incidents for a potential homicide referral to the county district attorney.

Rose did not have a weapon on him when he was shot, officials have said. On Friday, Allegheny County District Attorney Stephen Zappala told reporters at his office that Rose was found with an empty 9-millimeter clip in his pocket.

Officials said they found two guns in the car, which they said they were confident was the same vehicle that had been involved in the drive-by shooting. Amie Downs, a spokeswoman for the county police, said she did not know if the weapons found in the car were the same caliber used in that shooting.

Zappala said that the 20-year-old driver of the car, who police had interviewed but later released, may be charged with a crime later.

"I'm not sure that it was appropriate to release him," Zappala said.

He said that there was very good evidence from the crime scene of the drive-by shooting in North Braddock that preceded the officer's shooting.

"There's video, in fact there's video from a bus. There's video from a stationary camera," he said. "It's good evidence and then it explains exactly what happened in North Braddock."

Rosfeld did not initially cooperate with police, Zappala said but he was hopeful the interview would happen by the end of the day on Friday. It was not immediately clear if it had.

Pat Thomassey, who is Rosfeld's lawyer according to Zappala's office, did not respond to a request for comment from The Post.

The East Pittsburgh Police Department declined on Thursday to provide details about the officer.

The shooting has prompted calls by some activists for the state's attorney general to take over the case from Zappala, whose office's work overlaps with that of the East Pittsburgh Police Department as well as many other departments in the county.

"Our local district attorney has an inherent conflict of interest and by that we mean that he has to depend on an ongoing basis and testimony and cooperation and support of police officers for other prosecutions," said Tim Stevens, chairman and CEO of the Black Political Empowerment Project in Pittsburgh. "When they have to intentionally prosecute one of the people in blue, it could produce negative reactions from other officers."

Zappala acknowledged the potential for the appearance "of some kind of conflict," because of that, but said that it was up to the state legislature to change the procedure around police-involved shootings.

Police have fatally shot at least 495 people in 2018, according to The Post's database of the shootings, but Rose appears to be the first person to be killed by the small police force in East Pittsburgh since 2015, when the data collection began. Even as outrage and attention generated by police shootings and other uses of fatal force has become a near-constant part of the news cycles in recent years, it is rare for officers to be charged, and rarer still for them to be convicted.

Zappala estimated that he had charged more than 150 police officers for various offenses during his tenure as district attorney, and cleared seven of the nine police officers his office has reviewed over the use of deadly force.

"The police community, as any other aspect of our community, they have problems," he said. "I'm not looking for a particular conclusion, I'm not looking to protect anybody to the extent that people would suggest that. There's some people in this community that just if a police officer uses deadly force, then he's committed a criminal act. That's not the way the law is written."

The Allegheny County police also denounced some local media accounts citing anonymous "police sources" about a video that purportedly shows Antwon Rose firing a gun during the drive-by incident and that gunshot residue was found on his hands.

"While ACPD does have a video showing the North Braddock incident, that video does NOT show Antwon Rose firing a gun," it said in a statement on Friday night. "The information about gunshot residue is also false. Crime Lab reports are still pending and have not yet been issued."

People who knew Rose have stepped forward with kind words in recent days.

Family attorney Fred Rabner said the clip discovery after the shooting should not be conflated with a reason to use deadly force. Civil rights attorney Lee Merritt, who is also representing the family, has said he's struggled to find any justification for the shooting.

"These facts, without more, simply leave very little room to justify the use of deadly force by this officer."

On Friday he shared a poem written by the teenager.

"I am confused and afraid / I wonder what path I will take," it read. "I hear that there's only two ways out / I see mothers bury their sons / I want my mom to never feel that pain."