A federal jury deliberated for four days before returning with a verdict, reports CBS station WDJT.
Federal prosecutors said the four were part of a group of off-duty officers who beat Frank Jude Jr. in October 2004 outside a housewarming party for one of the officers.
The jury that included one black man convicted fired officers Jon Bartlett, 35, Daniel Masarik, 27, and Andrew Spengler, 28, of violating Jude's civil rights and conspiring to assault him while acting as officers.
Suspended officer Ryan Packard, 27, was acquitted of both charges.
An all-white jury acquitted Bartlett, Masarik and Spengler of most state charges last year. Hundreds marched through downtown in protest.
Six months later, federal prosecutors charged those three and Packard, as well as four others, who have pleaded guilty to similar federal charges.
Jude went to Spengler's home with Lovell Harris, 34, who is black, and two white women. He testified during the federal trial that a group of men surrounded their truck as they left and dragged him out.
Someone in the group punched him repeatedly and kicked him in the groin, causing him to black out at least once, Jude testified. The beating continued even after on-duty police arrived.
Jude testified that he recognized Spengler's voice as the person who threatened him while a gun was put to his head, but acknowledged he didn't see who it was. He also said he couldn't identify the people who beat him.
Other witnesses said the four officers punched or kicked Jude.
The police department disciplined 13 officers after the incident, including nine who were fired. Two of the fired officers won back their jobs.
Jude and the others who were with him have sued the officers and the city in federal court.