Court documents show 24-year-old Ethan Kollie will be in court Wednesday. No details of his plea agreement have been disclosed.
Kollie is accused of lying on a federal firearms form and possessing a gun while using illegal drugs.
Authorities have said there's no indication Kollie knew his friend Connor Betts was planning the Aug. 4 shooting in Dayton that killed nine people before police killed Betts.
The handgun Kollie is charged with illegally purchasing wasn't used in the shooting.
Investigators said Kollie told them he bought the body armor, a 100-round magazine and a part for Betts' gun.
A message seeking comment was left Saturday with Kollie's attorneys.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.