An inmate at the Iowa State Penitentiary has been found guilty of voluntary manslaughter following a deadly assault on another inmate in the prison’s kitchen.
Anthony Michael Koehlhoeffer, 35, was originally charged with second-degree murder after the December 19, 2024 assault that led to the death of fellow inmate Gregory Showalter, who was 64 at the time.
According to investigators, both men were working assigned cleanup duties in the prison kitchen near the end of their shifts when a verbal argument began. Surveillance video showed the confrontation escalating after Koehlhoeffer turned to walk away while Showalter continued speaking. Koehlhoeffer then turned back, pushed Showalter, and knocked him to the floor.
Prosecutors said Koehlhoeffer then stood over Showalter and carried out a violent attack lasting about 25 seconds. During the assault, Koehlhoeffer shoved Showalter once, punched him in the head 21 times, and kicked or stomped his head and face seven times. Investigators said eight of the punches and six of the stomps occurred after Showalter had already lost consciousness. Video review showed that Showalter never attempted to strike Koehlhoeffer during the altercation.
Showalter was first treated for his injuries and later transported to University of Iowa Health Care Medical Center, where he died on December 28, 2024.
On March 5, a jury found Koehlhoeffer guilty of voluntary manslaughter, a Class C felony under Iowa law. The conviction carries a maximum sentence of 10 years in the custody of the Iowa Department of Corrections, with no mandatory minimum before parole eligibility.
Koehlhoeffer was already serving prison sentences for robbery and assault on corrections officers and will continue serving those sentences.
The investigation into the assault was conducted by the Iowa Division of Criminal Investigation, and the case was prosecuted by the Lee County Attorney’s Office.
Koehlhoeffer’s sentencing hearing is scheduled for March 27, 2026.
