Protesters have rallied for a second day of demonstrations following the death of an unarmed black teenager, who was shot by police as he ran away from a vehicle he had been stopped in.

Antwon Rose II, 17, was shot three times by a police officer in East Pittsburgh as he ran from the vehicle on Tuesday. The officer, whose name has not been released, had been sworn into the police department just a few hours prior to the incident.

The protesters first took to the street on Wednesday evening, and fresh protests followed on Thursday in front of the Allegheny County court house.

A video posted on social media, that was captured by a bystander, appears to back up the official description of the circumstances presented by Allegheny County Police Superintendent Coleman McDonough, who said that Antwon and another individual ran from the vehicle after an officer ordered the driver to get out.

Mr McDonough confirmed to police that Antwon was unarmed, and said that two semi-automatic handguns were later found on the floor of the vehicle. Police have indicated that they believe the car was connected to a drive-by shooting they had been investigating.

The driver was arrested, but released without charges. He said had been operating as a jitney driver — a service similar to a taxi. A third person on the scene had not been immediately apprehended by police, who have asked that he turn himself in.

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“I understand in today’s atmosphere anytime a young man is killed there’s cause for outrage in some areas,” Mr McDonough told reporters on Wednesday. “However, I would urge people to give us time to conduct an objective investigation”.

Antwon was a “generous, hard working and highly promising student”, his family said in a statement.

“These facts, without more, simply leave very little room to justify these of deadly force by this officer,” the family said in the statement, which was provided by civil rights activist and attorney S Lee Merritt, who is representing the family. “Additional information concerning the background of the offending officer and the facts available to him at the time of time of the shooting is needed as we determine the appropriate action in this manner”.

Antwon, an honour roll student at Woodlands High School, had a “million-dollar smile,” Superintendent Licia Lentz told CNN, adding that he was “a very bright young man” who was enrolled in advanced placement classes.

“From all accounts, he was a generous, hard-working and highly promising student,” Ms Lentz said. “He had this million-dollar smile. He was gifted and teachers were really trying to mentor him.”

Protesters have called to oust District Attorney Stephen A Zappala Jr, but it is not clear whether charges will be made against anyone surrounding the incident where Antwon was killed.

A statement from Mr Zappala’s office said that he had met with Mr McDonough, and the investigation is ongoing.