A judge found James Mandarino, 42, guilty of aggravated battery and official misconduct. He had no comment as he left the courthouse after the verdict was read.
A videotape shows Mandarino repeatedly striking Ronald Bell with his baton after an early-morning traffic stop on March 28. Cook County Judge Thomas Fecarotta said he watched the tape 50 to 60 times.
"If a picture speaks a thousand words, the video speaks a million," Fecarotta said in court.
Mandarino chose to have a judge decide the case rather than a jury.
Judge Fecarotta called the beating unprovoked, unnecessary and unacceptable.
"We're very disappointed. We don't believe the evidence sustained the finding of the court. I'm very happy that the judge determined that the victim was drunk," Ed Wanderling, defense attorney, said.
Mandarino testified in court earlier this week that he saw Bell driving recklessly and followed him. Judge Fecarotta said the tape shows it took only 44 seconds from the time Mandarino saw Bell drive past until the officer had his gun drawn.
Moments before Mandarino struck Bell, he used a stun gun on passenger Nolan Stallbaum twice. "I kept my faith in the justice system and today justice prevailed," said Stallbaum Wednesday.
Judge Fecarotta said Bell was probably drunk at the time of the attack nearly a year ago in Bell's own driveway, but the judge said that does not justify the fact Mandarino struck Bell 15 times with his baton.
"There's no getting around the tape. That is the best evidence that the judge had," prosecutor Virginia Bigane said.
Defense attorneys argued Mandarino feared for his life because Stallbaum and Bell were drunk and uncooperative. Prosecutors say Mandarino was a good officer until March 28th, when he just snapped.
"This finding sends a message that these types of offenses committed against unarmed civilians and citizens is a breach of the public trust and will not be tolerated," Michael Gerber, prosecutor, said.
Bell was not in court for the reading of the verdict Wednesday, but his brother, Stacy, who witnessed the attack, spoke.
"I saw my brother getting viciously beaten by someone I couldn't do anything to," Stacy Bell said.
Bell and Stallbaum have filed civil suits in the attack.
Mandarino is out on bond until his sentencing, which is scheduled for April 25. He faces 2 to 5 years in prison.