David Sidener, 52, was awaiting trial for murder.
The Evansville, Indiana native now faces additional charges of possessing contraband in a penal institution.
He allegedly hoped to make a deal to have the murder charge dropped in exchange for revealing the location of the bullets and gunpowder.
Investigators found the ammunition hidden inside a film projector and a CD player in a room at the jail.
They are questioning a Cermak Hospital therapist who used that room to meet inmates.
