As the U.S. Department of Justice begins a civil investigation into the practices of the Chicago Police Department, the trial of a high-ranking officer accused of assaulting a man with his gun while on duty in 2013 began Tuesday morning with testimony from the alleged victim.

Commander Glenn Evans, a 30-year veteran of the force, is accused of shoving a gun into Rickey Williams' mouth, holding a Taser to the man's groin and threatening to kill him if he did not tell Evans where his gun was. Despite Williams' claims, Evans has a crowd of supporters, which includes neighbors and community leaders.

In court Tuesday, Williams testified that Evans forced the gun as far down his throat as his Adam's apple, saying that it was painful. Many of the other details of the encounter, Williams found difficult to recall. He said another officer punched him twice, but under cross examination, he admitted they were light taps and said he could not remember which officer it was.

Williams also admitted that he may have gotten it wrong when he first described the incident to investigators, saying Evans held the gun in his left hand. The defense alleges Williams changed his recollection to the right hand after prosecutors told him Evans was right-handed.

In August, a judge ruled that DNA taken from the gun could be submitted as evidence during Evans' trial. Prosecutors say the swab had DNA from Williams, whom Evans chased into an abandoned house in January 2013. The defense says the DNA could easily have come from Williams touching the gun during his arrest.

When the defense entered Evans' silver .45-caliber semiautomatic into evidence on Tuesday, Williams said he did not recognize it. In previous statements, Williams described the gun as black.

According to details revealed last month in the prosecutor proffer, Evans claimed he saw the then-22-year-old Williams with a gun on the 500 block of East 71st Street in January 2013. Evans chased Williams into a home, tackled him, then shoved his pistol into Williams' mouth and made threats.

Evans and other responding officer officers took Williams into custody, but no gun was ever found, prosecutors said.

Laura Morask, Evans' attorney, said in September 2014 that investigators had yet to interview Evans about the case and get his side of the story.

"Something you always do before a case is charged is you ask the suspect their account, but that was never done," Morask said.

Evans was stripped of his police powers and charged with official misconduct and aggravated battery. In 2012, NBC 5 reported that Evans was among a small group of officers who had been repeatedly accused of police brutality and misconduct, resulting in millions of dollars in tax-dollar payouts.

Williams was later charged with a misdemeanor offense of reckless conduct based on his alleged possession of a gun, but that charge was dropped on April 24, 2014, when officers failed to appear in court to testify.

A day after his arrest, Williams filed a complaint with the Independent Police Review Authority describing the incident. On Feb. 1, 2013, IPRA ordered Evans to turn in his weapon for forensic testing.

DNA from Evans' weapon came back as a match to Williams more than two months later, and IPRA recommended that Evans' police powers be stripped.

Evans' attorney claims the IPRA investigator who recommended the commander be taken off duty had a personal bias against Evans that originated years before the incident involving Williams. This alleged bias could be key in the defense's case.

In the South Side community where Evans lives, neighbors have said they support the man who kept their community safe.

"I've known him since he was 6 or 7 years old," Barbara McNeal said last year. "If it wasn't for Glenn Evans, our block probably would be drug-infested, gang-banging and everything else."