ATLANTA—A Georgia police officer was fired Thursday, less than 24 hours after authorities say he kicked a handcuffed man in the head.

Master Police Officer Robert McDonald “stepped outside the guiding principles of our agency,” a statement from the Gwinnett County Police Department says.

“What happened yesterday was clearly outside of state law and department policy,” the statement says. “We do not tolerate actions that are not consistent with our core values or state law.”

The police department also has initiated a criminal investigation of McDonald’s behaviour and the results will be turned over to the county district attorney, who will decide whether to prosecute McDonald.

A working phone number could not immediately be located for McDonald, and it wasn’t clear whether he had an attorney who could comment on his firing.

McDonald assaulted the man as he responded to a call to help a supervisor with a traffic stop in Lawrenceville, just outside Atlanta, around 4 p.m. Wednesday, police said in an emailed statement.

An ambulance crew then arrived and treated the handcuffed man, who has been identified as Demetrius Bryan Hollins.

McDonald’s shift commander initiated an “immediate investigation,” police said. The officer was sent home on administrative leave and his department-issued gun was taken.

The incident was captured on cellphone video by a witness stuck behind the stopped car and the police vehicle. Police statement says the video is “very disturbing and speaks for itself” and was “very crucial to the investigation and it confirmed that the force used was unnecessary and excessive.”

The video, which was posted online, shows an officer appearing to yell orders at a handcuffed man who then lies face-down in a left-turn lane of the busy intersection. A second officer runs up and immediately appears to stomp on the man’s head before both officers eventually pull him to his feet.

In a booking photo, Hollins appears to have blood on his nose and lip.

Jail records show Hollins faces charges of driving with a suspended or revoked license, operating a vehicle with a suspended or revoked registration, failure to signal, having a brake light that’s not in good repair, obstructing a law enforcement officer and having less than an ounce of marijuana. He was being held Thursday on bond totalling $7,502.

The two officers are white and Hollins appears to be black, police Cpl. Michele Pihera said in an email.