Koehlhoeffer convicted of manslaughter in ISP assault

FORT MADISON - On December 19, 2024, Anthony Michael Koehlhoeffer, 35, an inmate at the Iowa State Penitentiary (ISP) was charged with Murder in the Second Degree, a Class B Felony, in violation of Iowa Code Section 707.3(1) of the Iowa Criminal Code. The charges stemmed from allegations that Koehlhoeffer committed a violent assault on another inmate, Gregory Showalter (then 64), while both individuals were inside the ISP kitchen. Video surveillance footage from ISP revealed the following:
‘Immediately prior to the assault, both individuals bad been working on assigned tasks of cleaning up areas of the kitchen prior to the end of their regular respective shifts. At approximately 4:05:05 PM, an interaction between Keohlhoeffer and Showalter begins, which eventually devolves into an apparent verbal argument. At approximately 4:07:03 PM, Koehlhoeffer turns and begins walking away from Showalter as Showalter appears to continue speaking at Koehlhoeffer. Koehlhoeffer then turns back around, approaches, and pushes Showalter, who stumbles and falls to the floor. Koehlhoeffer then walks to where Showalter is lying, stands over him, and begins punching, kicking, and stomping Showalteer's head/face area. Over the course of the approximately 25-second physical assault from Keohlhoeffer sustained by Showalter, Koehlhoeffer strikes Showalter once with a two-handed shove to the jaw and face area, 21 punches to the head, and 7 kicks/stomps to the face and head area. It should also be noted that 8 of the punches and 6 stomps/kicks appear to have been sustained after Showalter had lost consciousness. At no time during the review is Showalter ever observed attempting to strike (or striking) Koehlhoeffer in any way.’
Showalter received initial medical treatment and was subsequently transported to the University of Iowa Health Care Medical Center where he ultimately succumbed to his injuries on December 28, 2024.
On March 5, 2026, Anthony Koehlhoeffer was found guilty of Voluntary Manslaughter, a Class C Felony, in violation of Iowa Code 707.4, by a jury of his peers. Voluntary Manslaughter carries a maximum sentence of 10 years within the Iowa Department of Corrections, with no mandatory minimum prior to parole eligibility. Koehlhoeffer will remain in the custody of the Iowa Department of Corrections until his sentencing hearing on March 27, 2026. He will continue to serve his underlying sentences in the Iowa Department of Corrections for Robbery and Assault on Corrections Officers.
The Division of Criminal Investigation (DCI) was the responding agency and led the investigation on the case. This matter was prosecuted by the Lee County Attorney’s Office.