(AP) – A 56-year-old man who is already in jail solved a 17-year mystery when he pleaded guilty to killing a northwest Missouri woman.

Michael Wilson pleaded guilty Thursday to killing 36-year-old Therese Campen of Raytown in February 1996. Prosecutors say Campen gave Wilson a ride to a bus stop in Raytown and Wilson later called her and made a date.

Wilson told an Andrew County judge Thursday that he planned to kill Campen. He strangled her and dumped her body in a cemetery near Amazonia, after hitting her with a piece of a broken gravestone to make sure she was dead.

Wilson is serving three 20-year sentences for convictions from Jackson County. He was sentenced to life in prison without the possibility of parole.