A Pittsburgh police officer has been charged with criminal homicide in the fatal shooting of an unarmed black teenager.

The Allegheny County, Pennsylvania district attorney charged East Pittsburgh police Officer Michael Rosfeld in the death of 17-year-old Antwon Rose II on Wednesday. The high-school honours student died last week after Mr Rosfeld shot him three times in a traffic stop, according to the criminal complaint.

Mr Rosfeld was released on Wednesday morning on $250,000 bail, his lawyer told local news station WPXI. A preliminary hearing was set for 6 July. He has yet to enter a plea.

"This is a small stride toward justice but we have a very long road ahead," the Rose family’s attorney, Lee Merritt, tweeted. He added: “The family will settle for nothing less than a conviction and appropriate sentencing.”

Antwon was riding with two friends in a silver Chevy Cruze last Tuesday when police pulled the teenagers over. Officers later said the vehicle matched the description of one connected to an earlier shooting.

When police ordered the teenagers out of the vehicle, the department said, the group attempted to run. That’s when Mr Rosfeld opened fire, striking Antwon three times – including once in the back, according to the complaint.

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Video from the scene posted to Facebook shows shots being fired as the teenagers run from the car. A witness can be heard gasping and asking: "Why are they shooting at them?"

According to the complaint, Mr Rosfeld at first told detectives that he saw something he "perceived as a gun” in Antwon’s hand as the teenager emerged from the car. Later in the same interview, he allegedly told officers he did not see a gun.

Mr Rosfeld was sworn in to the police force just hours before the shooting, but had worked with other local departments for seven years, according to WPXI. He has been on administrative leave since the day of the shooting.

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The shooting death sparked days of protests in Pittsburgh, where protesters carried signs reading: “3 shots in the back. How do you justify that?”

Allegheny County Police Superintendent Coleman McDonough said in a news conference that the shooting could be justified if the officer thought there was an imminent threat of death, or if the suspect posed a threat.

Mr Merritt responded that the teenager posed “no immediate threat to anyone,” as police have admitted he was unarmed at the time of the shooting. Officers later found two semi-automatic firearms on the floor of the car.

Zaijuan Hester, another teenager in the car that day, was charged on Wednesday with criminal attempted homicide in connection with the earlier drive-by shooting. He has yet to enter a plea.

At a press conference on Wednesday, Allegheny County District Attorney Stephen Zappala said Antwon was in the car for the drive-by shooting, but was not a suspect.