From [DailyHerald] A Black Metra police officer faces charges of aggravated battery after a video he gave to prosecutors showed him beating and punching a Black man at a Chicago train station.

David Robertson, 50, of Matteson, told Metra officials the 45-year-old man he arrested on charges of trespassing started the fight in 2015 at Millennium Station, authorities said.

But a surveillance video shows Robertson striking the man in the face unprovoked, spraying pepper spray at him and smacking him with a baton as two other officers joined in, Cook County prosecutors said.

Robertson's attorney Shay T. Allen said Robertson is innocent.

An investigation into the arrest was sparked by a video that Robertson filmed with his phone while watching a playback of surveillance footage in the company of other Metra police officers who laughed and offered a running commentary of the beating.

"You got him!" one police officer said during the viewing.

Robertson, who could not be reached for comment, turned over his video to Cook County assistant state's attorneys who informed Metra on Nov. 9, 2016, that Robertson might have provided false testimony because the images contradicted his version of events.

Robertson was released after an appearance in Cook County bond court Monday. He also was charged with perjury and official misconduct.

Allen said the state's attorney's office was being "overzealous."

"Mr. Robertson was working in his capacity as a police officer. I am expecting he will be fully exonerated of all charges," Allen said, adding that Robertson had served for 25 years with no previous complaints.

But "as an agency that now prides itself on having a well-run and professional police force, and after our own investigation into the matter, we are disturbed and deeply troubled by this conduct," said Metra Executive Director Don Orseno.

After being contacted by the state's attorney's office, Metra began an internal investigation. On Nov. 10, Robertson and a second officer who participated in the arrest were suspended without pay. Both were fired on Dec. 28.

A third officer who took part in beating the man was dismissed before the internal investigation.

Of the officers who were heard laughing in the background on the video, two were disciplined and two no longer work at Metra, spokesman Michael Gillis said.

Robertson testified the other man started the fight and "rushed" him, then reached into his right pants pocket, which led the police officer to pull out the pepper spray. The confrontation began around 9 p.m. Jan. 15, 2015, as the man sat on a bench. Robertson initially told the man he needed to leave if he didn't have a ticket and the man refused. Both exchanged words.

Prosecutors state Robertson punched the man in the face and aimed pepper spray at him without any physical aggression on the 45-year-old's part and the video backs up that version. The video also shows backup officers arriving and the man being pummeled with batons. Robertson later punches him in the face, the video shows.