VALLEJO, Calif. -- A California police officer is under investigation and on administrative leave while the Vallejo Police Department determines if he used a racial slur during a traffic stop.

The investigation was announced after a witness provided CBS San Francisco video of the incident, which took place Saturday morning near Sonoma Boulevard in the city of Vallejo.

Leo Bruno says he recorded the encounter from inside his home. He told CBS News that he heard the officer shout the n-word. "It sounded pretty clear to me as I was filming, though, some who've watched it have had a little trouble hearing it," he said Sunday.

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While filming the traffic stop, Bruno says he was reminded of recent fatal police shootings of black men across the U.S.

"All the fatal shootings over the past year, like, [Philando] Castile, [Michael] Brown and Trayvon Martin," he said Sunday. "We were worried it was going to happen again right on our doorstep."

A police officer is under investigation while Vallejo Police Department determines if he used a racial slur during a traffic stop. Courtesy of Leo Bruno

In the footage, two officers with their guns drawn can be seen outside the vehicle while two men sit inside with their hands up, outside the windows. Just a few moments later, one officer begins shouting.

"They proceeded to handcuff the occupants of the vehicle and lay them on the ground and search them," Bruno told CBS San Francisco. "I thought it was potentially another [police] shooting incident and I was nervous that the gun was going to go off and they were going to shoot the driver."

"It's always unnecessary and uncalled for and just racist to say things like that," he added.

CBS San Francisco showed the video to Vallejo Police Lt. Kenny Park and asked if he supports officers who use racial slurs.

"I think you know the answer to that -- the answer is no," said Park.

The Vallejo Police Department sent a statement to CBS San Francisco on Sunday announcing an internal investigation into the officer's actions. They did not identify the officer.

"The citizen reports the officer used an unacceptable racial epitaph during the initial contact," the statement read. "The Vallejo Police takes all reports of unprofessional behavior seriously and has no tolerance for such behavior. The Chief of Police has ordered an immediate investigation into the incident."