Jason Katz, who was sentenced to federal prison for illegally selling a gun to the man who shot and killed South Bend Police Corporal Nick Polizzotto, died from injuries suffered in a prison altercation.

Katz, 32, of South Bend was serving his nine-month sentence at the Metropolitan Correctional Center in Chicago. He was scheduled to be released in August.

An ambulance took Katz to a Chicago area hospital sometime after the altercation Tuesday afternoon. He died around 7 a.m. Wednesday.

Katz pleaded guilty to selling a 22-caliber handgun to Scott Barnaby at an April 22 gun show. The charges alleged Katz didn't perform a national background check on Barnaby, didn't take down his name or any other type of personal information and made a false report into his sales record.

Barnaby used that gun to fire off shots near the Landing night club on Lincoln Way East. When officers arrived on scene, Barnaby used a different gun to shoot Patrolman Michael Norby and Corporal Nick Polizzotto.

Polizzotto died from his injuries. Police returned fire and killed Barnaby.

South Bend Police learned of Katz's death on Wednesday and were stunned.

"If you trace this back to its very beginning, it's just unbelievably bad circumstance after circumstance," said Capt. Phil Trent, of the South Bend Police Department. "It's just another case where one bad thing leads to another."

The FBI is investigating Katz's death. No other details were released.