CHICAGO (Reuters) - A Chicago police commander who had been praised for his crime fighting in some of the city’s roughest neighborhoods “crossed the line” into criminal conduct when he put a gun in a suspect’s mouth, a prosecutor said on Tuesday.

Glenn Evans, relieved of his duties last year pending the outcome of his case, went on trial in Chicago on Tuesday for aggravated battery and official misconduct in the Jan. 30, 2013 arrest of Rickey Williams, 25. Both men are black.

Evans’ actions had “no legal justification,” Cook County Assistant State’s Attorney Frank Lamas told Judge Diane Cannon at the start of the bench trial.

“The defendant clearly crossed the line, hiding behind his badge and commander’s title,” Lamas said. Evans also put a Taser to Williams’ groin during his arrest for reckless conduct, prosecutors said.

Evans’ trial comes a day after the U.S. Department of Justice said it was conducting a civil rights investigation of the third-largest U.S. city’s police department, including its use of force.

The amount of force that can be used by police officers has become a focus of national debate due to a series of high-profile police killings of black men in U.S. cities.

Evans’ defense attorney, Laura Morask, said Williams had originally named another officer, and that the case was “built on nothing.” Morask said Williams showed no signs of injury to his mouth from the alleged assault.

Williams took the stand on Tuesday, saying often that he did not recall details from the arrest or subsequent interviews with investigators.

Evans has been the subject of several police misconduct lawsuits, according to local media reports.

The city has had nearly two weeks of protests following the release of a video of the shooting death of a 17-year-old black teen by a white police officer in 2014. The officer, Jason Van Dyke, was charged with murder in the shooting of Laquan McDonald on the same day the video was released.

On Monday, prosecutors said they would not seek criminal charges in another 2014 police shooting that caused the death of Ronald Johnson III, also caught on video.

Chicago police released another video on Tuesday that showed a man in custody being Tasered and dragged from his cell by his handcuffs in 2012.

Mayor Rahm Emanuel said that the treatment of Philip Coleman, who later died at a hospital, was being investigated. His family has sued the city.