CHICAGO (CBS) — Paul O’Neal, the black teenager who was killed by Chicago police, died of a single gunshot wound to the back, the Cook County medical examiner’s office confirmed, in an autopsy report released Wednesday.

It showed the teen didn’t have any illegal drugs in his system.

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A Chicago police officer shot and killed O’Neal July 28, in an incident that was partly captured on video. The medical examiner’s office report stated that O’Neal was seen driving a 2002 Jaguar near 74th and Merrill. The car had been reported stolen.

O’Neal, 18, reportedly refused to stop the vehicle and “rammed head on” into a marked squad car, injuring two officers. After impact he got out and ran.

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The medical examiner’s office report says, “During the foot pursuit shots were fired by other unidentified officers on the scene and possible by O’Neal,” though it was later determined that O’Neal was unarmed.

Believing the shots were fired by O’Neal, an officer fired his “Glock 9mm handgun five times in an attempt to stop the threat,” the report states.

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O’Neal was struck by a single bullet in the right side of his back, according to the report.