Investigators have opened a case against a police officer who was caught on camera beating a peaceful protester at a banned opposition rally in St. Petersburg on July 31.

The unidentified officer is under investigation on suspicion of exceeding his authority and, if charged and convicted, could face up to 10 years in prison, the Investigative Committee said in a statement carried by Interfax.

A video of the beating was uploaded onto YouTube on the day of the incident.

The Investigative Committee asked witnesses to provide additional video footage of the officer's actions.

The officer was filmed calling protesters “ferrets,” shouting profanities and attacking one of the rally's participants, grabbing him by the hair and hitting him on the head with a rubber baton.

His actions caused an outcry on the Internet, where bloggers launched a campaign to identify and prosecute the officer, whom they nicknamed “Pearl Ensign” because of a pearl bracelet that he was wearing.

On Tuesday, St. Petersburg city police said they had identified the officer and punished him with an official reprimand, local news web site Fontanka.ru reported.

The officer's superiors may also face penalties over his actions, the report said.

The officer claimed that he was reacting after a protester called him “a ferret and a gray mouse,” but his excuse has been dismissed as insufficient, it said.