A D.C. police officer involved in the 2016 shooting of motorcyclist Terrence Sterling is under investigation again, this time for alleged “improper conduct” during an arrest, according to the Metropolitan Police Department. Sterling’s death sparked weekly protests in the District and also resulted in a grand jury investigation from the U.S. Attorney’s Office. Palmer received a 20-day suspension for his role in the death, while his partner was fired for shooting and killing the 31-year-old unarmed black man.

The Washington Post was the first to report on the new investigation into Palmer.

The five-year MPD officer is currently on administrative duty as the department investigates his behavior during the December 5 arrest of a man charged with possession of an open container of alcohol and resisting arrest, according to the Post. The man was arrested on the 1900 block of Second Street NW, according to a police report obtained by the outlet.

Police say the man became combative with officers when they tried to stop him for an open container. The man was thrown to the ground and suffered a broken bone. Palmer is not being investigated in relation to any of the injuries the man sustained, the Post reports. Two unnamed officers familiar with the investigation told the outlet that Palmer used profanity during the arrest and pulled out his baton. The investigation will determine whether Palmer was threatening the man with his baton.

Palmer was driving the police cruiser that chased Terrence Sterling for 25 blocks in September 2016. He and his partner, Brian Trainer, later reported that they saw Sterling speeding and running red lights on his motorcycle. It’s against department policy to give chase for a traffic violation, but Palmer chased Sterling anyway, eventually blocking his path.

The officers said that Sterling tried to drive his motorcycle into the side of the police cruiser, and that Trainer shot him twice out the passenger-side window because he feared for his life. Some witnesses contradicted that account. Trainer didn’t have his body-worn camera turned on during the incident. The U.S. Attorney’s Office opened a grand jury investigation into the shooting, but eventually declined to charge Trainer. He was fired from the force, and lost his attempts to appeal his discharge. Palmer, however, remained on the job.