An arrest by BART police has sparked claims of excessive force after video depicting an officer punching a handcuffed and prone African American man in the face went viral. CBS 5 reports that this all went down Friday at the Embarcadero BART station, and that officials and witnesses are telling two very different versions of what transpired.

A BART spokesperson told the channel that police were responding to reports that a man threatened to rob a passenger, and defended the actions of the agency's officers. Tarina Larsen, who shot the above video and posted it to Facebook, tells a very different story.

"I just watched 4 BART officers arrest 2 Black children at the Embarcadero Station after an old white male antagonized them with racial slurs and then had the audacity to call the cops on them knowing damn well what will happen to those kids next," wrote Larsen. "Witnesses are frantically trying to explain this to the cops as two of them are holding the kid down on his stomach and jamming his knee into his back. They flip him over and another knee is jammed into his ribs."

"At one point the same cop looks like he's about to pummel the kid for squirming and the only reason he doesn't is because we've got eyes on him," she continued.

ABC 7 reports that BART Police claim they believed the man was armed, but no weapons were found.

"It was a brutal scene, my knees were shaking," witness Pamela Martinez told ABC 7. "One of the policemen had his knee on the kid's back. And it looked like he was going to break it. And one guy next to them yelled, 'please just get your knee off the kid's back, you're going to break it.' "

Martinez also captured the arrest on video and posted it to Facebook. "This hell of a scene took over 10 minutes," she wrote. "10 minutes of begging and yelling for justice without anything happening. At one point, everybody suddenly stepped away and we saw that the cop pulled out a gun (WHY?!?!). My legs trembled as I was sure that the cops were gonna open fire on these kids."

The video bears some resemblance to the 2009 New Year's Day bystander video depicting the shooting death of Oscar Grant at the hands of BART Police. Johannes Mehserle, the officer that shot Grant, served an eleven month prison sentence for the killing.

According to CBS, the unidentified man was booked on five counts of battery on a police officer and two counts of resisting arrest. BART’s Internal Affairs Division, meanwhile, is investigating.

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