(CNN) Hours after being sworn in on the local force, a suburban Pittsburgh officer fatally shot an unarmed 17-year-old who ran when police stopped a vehicle that was suspected to be involved in an earlier shooting, authorities said.

The Allegheny County Medical Examiner's Office and a family attorney identified the victim as Antwon Rose II of Rankin. Antwon, an African-American, died at a hospital. He had been a passenger in the car, which authorities suspected of being involved in a shooting earlier Tuesday in a nearby community, Allegheny County police said Wednesday.

Protesters on Wednesday converged on East Pittsburgh, the borough southeast of Pittsburgh where the shooting occurred.

Sometime before 8:30 p.m. Tuesday, someone fired nine .40-caliber rounds at a 22-year-old in North Braddock borough, Allegheny County police said. The victim, who returned fire, was struck and taken to a hospital. He was treated and released.

Witnesses, including one who flagged down a police officer, described the vehicle in the shooting. Thirteen minutes later, an East Pittsburgh officer saw a silver Chevy Cruze, which matched the vehicle's description, police said. The officer stopped the car around 8:40 p.m.

The officer ordered the driver out of the car and onto the ground, police said. Antwon and another passenger "bolted" from the vehicle, and the East Pittsburgh officer opened fire, striking Antwon, Allegheny County police said.

Reggie Shuford, executive director of the ACLU of Pennsylvania, said Thursday it appears the East Pittsburgh officer "disregarded the basic humanity of this boy."

"Fleeing from a scene does not give law enforcement the right to indiscriminately shoot young boys or anyone. No one, especially children, should ever fear death at the hands of police. Lethal force should be an absolute last resort, not a first option," his statement said.

In a news conference, Allegheny County Police Superintendent Coleman McDonough said the shooting could be justified if the officer thought there was an imminent threat of death -- to the officer or others -- or if the fleeing suspect posed a threat. But, he said, the district attorney will ultimately decide if it was a justified use of force.

The officers involved weren't wearing bodycams, he said.

'All they did was run'

A witness to the shooting captured it on video that was posted on Facebook.

In the video, a police SUV is seen stopped in the middle of the street as another police car pulls up behind it. Two people are seen running from the Chevy Cruze. Within seconds three shots ring out. The runners appear to drop to the ground.

The woman recording the video says, "Why are they shooting at him?"

"All they did was run and they're shooting at them," the woman said.

The 20-year-old driver of the vehicle was later released, police said. Authorities are still searching for the other passenger.

Antwon was unarmed, McDonough told reporters. Two semiautomatic firearms were recovered from the floor of the vehicle, he said.

McDonough said he was "very confident" the car carrying Antwon was the one involved in the shooting, pointing to "ballistic damage to the rear window."

Based on witness statements, McDonough said, he believes officers gave Antwon verbal commands, but he didn't know the specific command.

Police: Officer fired 3 times, victim struck 3 times

The East Pittsburgh officer fired three times, hitting Antwon three times in various parts of his body, McDonough said.

Allegheny County officials on Thursday identified the officer as Michael Rosfeld, according to an email from the county's director of communications, Amie Downs. CNN has attempted to reach Rosfeld numerous times, but has not been successful.

The officer has been placed on administrative leave, police said. McDonough said on Wednesday that he had not been interviewed.

Asked if the officer is white, McDonough said, "I don't understand what that has to do with the situation."

The officer had worked with other local departments for seven years, CNN affiliate WPXI reported. He had been sworn in that day on the East Pittsburgh police force, Mayor Louis Payne told the station.

Antwon Rose

Family attorney S. Lee Merritt said Antwon "posed no immediate threat to anyone" because he wasn't armed.

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

East Pittsburgh Police Chief Lori Fruncek , who leads a force of eight patrol officers, couldn't be reached Wednesday.

McDonough said he understands that "in today's atmosphere, any time a young man is killed, there's cause for outrage ... in some areas." He asked for patience with the investigation.

"Some of the initial postings on social media that came out directly after this incident were inaccurate and inflammatory," he said. "I would urge that people in the community give us a chance to conduct an objective investigation."

In a joint statement, Payne, East Pittsburgh police and council, said they were saddened by Antwon's death.

"This is a very stressful time for our community. We are seeking truth and answers but the process takes time. We hope that everyone can respect this process. We will get through this together as a community," the statement said.

'He had this million-dollar smile'

During the Wednesday protest on a rainy evening in East Pittsburgh, people shouted, "Justice now!"

The Woodland Hills School District confirmed Antwon had attended Woodland Hills High School.

"From all accounts, he was a generous, hard-working and highly promising student," Merritt said. Assistant Superintendent Licia Lentz of the school district said Antwon was "a very bright young man" who took advanced placement classes.

"He had this million-dollar smile," she said. "He was gifted and teachers were really trying to mentor him."

Gisele Barreto Fetterman, who owns the Free Store in nearby Braddock, where her husband is mayor, said Antwon volunteered at the shop during the summer of 2015 and regularly came back on Saturdays. She described him as an attentive, mature young man with "such great energy."

The store provides food, toys, clothes, backpacks and other items to members of the community, and Antwon would offer to entertain kids while their parents picked up what they needed, she said.

"He was just a really great kid. He had these really intense, big eyes. He was very smiley, very goofy," Fetterman said.

Antwon also worked at a gym where Fetterman's children took gymnastics classes, she said.

"I just expected he would always pop in and update us on what's going on. I think about how his life was cut short and all the things we won't see him do and all of the dreams we will never see him achieve and it's a really sad day," she said.