By Dana Kozlov

(CBS) – A Chicago police officer deliberately turned off a dashboard camera during a road stop and mistreated a motorist who had been pulled over, according new lawsuit against the department and the city.

CBS 2’s Dana Kozlov reports the suspect was no ordinary citizen.

It was a New Year’s morning and a Chicago police officer arrived as back-up for a traffic stop, with gun drawn. Not a minute later, he runs back to his squad car and turns off the dash board camera.

“It’s certainly more nefarious,” says lawyer Tim Fiscella.

That’s because, he says, it happened after officers realized they pulled over George Roberts, a supervisor with the Independent Police Review Authority — or IPRA — the agency responsible for investigating police misconduct.

Roberts was pulled over near Blackstone and 85th Place on suspicion of drunken driving. The newly filed federal lawsuit claims officers threatened, pushed and mistreated Roberts once that camera went dark.

Chicago Police Department dash-cam policy is clear, stating “during the recording of an incident, department members will not disengage the in-car video system until the entire incident has been recorded.”

The video must be preserved for 90 days, CBS 2 Legal Analyst Irv Miller says.

A police spokesman declined comment, citing the pending litigation.

Roberts was charged with DUI, but was found not guilty after his case went to trial.