A 48-year-old Casper man charged with holding his girlfriend captive for 20 hours and threatening to kill her has pleaded not guilty by reason of mental illness.

Peter Potter, who was arrested Feb. 7 after a three-hour standoff with police, is charged with kidnapping and aggravated assault. He entered his plea Thursday.

However, in April, Natrona County Circuit Judge Michael Patchen found Potter competent to stand trial.

A 55-year-old woman told police that Potter had held her captive for 20 hours, had beaten her with a hammer, kicked her with steel-toed boots, held a deer antler to her neck and threatened her with a knife. She said Potter wouldn't allow her to eat or drink anything and poured water on her to keep her cold and wet. She told police she escaped when Potter's mother came to visit.