The Billings Gazette reports that 34-year-old Jeffery Glen Haverty pleaded guilty Monday.
Haverty and 32-year-old Donald Ray Cherry were both charged with deliberate homicide in the October 2017 death of 41-year-old Myron Wesley Knight.
Prosecutors and Haverty's attorneys say they will seek 50 years in prison under a plea agreement.
Authorities say Knight asked a Billings casino employee to hold $120 in winnings before leaving with the men.
Police say Haverty robbed Knight of his remaining $6 and began decapitating him in a transient camp.
Authorities say Cherry took part in the decapitation after returning from a gas station.
Knight's body was found three weeks later.
Cherry's trial is scheduled to begin in July.
Information from: The Billings Gazette, http://www.billingsgazette.com
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