The Buchanan County prosecutor's office filed charges against Martin Lee Williams, 51, Thursday, including a class C felony charges of involuntary manslaughter and a class D felony charge of abandonment of a corpse.
According to the probable cause statement, Williams and Fisher were last together on Sept. 5 at his home in the 400 block of N. 17th Street in St. Joseph.
That is where detectives say Williams prepared a syringe containing a controlled substance for himself and Fisher.
A statement from Brett Kelley, a St. Joseph police officer, says Williams injected Fisher with the drugs and she became unresponsive.
Instead of calling for medical assistance, the statement alleges Williams built a wooden box and placed Fisher's body inside before taking it to a remote location in northern Platte County.
Someone found the box last week, with Fisher's body inside, and contacted authorities.
According to court documents, Williams has an extensive criminal history, including a warrant on file for burglary out of California.
He was also on parole in Kansas and was not to be living outside of the state.