(CNN) The unarmed 17-year-old who was shot and killed by police in East Pittsburgh earlier this week died of a gunshot wound to the "trunk," the Allegheny County Medical Examiner's Office said Friday.

The manner of Antwon Rose's death was listed as homicide.

The medical examiner's brief report did not specify in what side of the "trunk" Antwon was shot. Witnesses said the African-American teen was fleeing police when he was struck by bullets.

The officer who fired the fatal shots was identified by Allegheny County officials on Thursday 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 -- who had just been sworn in on the East Pittsburgh police force a few hours before the shooting -- has been placed on administrative leave, police said. He had worked with other local departments for seven years, CNN affiliate WPXI reported.

Allegheny County Police Superintendent Coleman McDonough said on Wednesday that the officer had not been interviewed.

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

What happened?

Antwon, who lived in nearby Rankin, had been a passenger in a car that was stopped by police Tuesday evening because it matched the description of a car that was involved in an earlier shooting, Allegheny County police said.

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.

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.

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

The police superintendent 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.

Teen's death prompts protests

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

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.

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In a news conference, 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.

Questions about the use of force

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.

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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."

'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."