Rajko Utvic, 37, was killed July 6 by officers responding to a 911 call from a man who said he had taken 100 Ibuprofen pills.
Police said the man refused to drop the knife, and he was shot when he came at officers Craig Klepel and Mathias Zinnen.
An investigation by the Racine County Sheriff's Office said witnesses confirmed the officers' accounts. They said officers tried to stop Utvic with electronic shock devices, but they didn't work. A summary of the report from Racine police said the investigation found Utvic suffered from mental illness. It didn't provide details.
The officers have returned to duty.