CHICAGO (CBS) — The trial begins Tuesday for a Streamwood police officer accused of brutality.

Fired officer James Mandarino was caught on his own squad car dashboard camera beating a driver during a traffic stop.

The video shows him hitting the driver more than a dozen times and firing a stun gun.

The beating victim, Ronald Bell, 28, required hospital treatment. He was left with a concussion, seven stitches to his ear and multiple contusions, according to the Cook County State’s Attorney’s office.

A passenger in the vehicle was stunned twice.

The videotape showed no evidence that the motorist or passenger ever resisted arrest or presented any physical threat to the officer, prosecutors said previously.

Earlier, the video from Mandarino’s squad car shows a brief pursuit – about 30 seconds – before the driver stops in front of his own home. Mandarino is shown ordering the driver and passenger out of the car with his weapon drawn, and they comply.

Mandarino’s attorney has argued that the car fled a traffic stop, and Mandarino didn’t know if the occupants had a weapon.

Mandarino was a 15-year veteran of the Streamwood police force. He is charged with aggravated battery and official misconduct, both felonies.

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