NEW ROCKFORD, N.D. (AP) — A North Dakota woman charged as an accomplice in the slaying of a Minnesota woman three years ago has been sentenced to serve 20 years in prison.

38-year-old Crystal Herman, of Bismarck, pleaded guilty in January in the 2015 death of 36-year-old Amanda Engst, who was originally from Breckenridge, Minnesota. She was sentenced Thursday.

Herman admitted to helping kidnap Engst on the Spirit Lake Indian Reservation in northeastern North Dakota and steal her car. Investigators believe Engst was beaten with a shovel, wrapped in a tarp and dumped in the Sheyenne River tied to a cinder block while still alive.

Herman was charged after being arrested with her husband for a string of robberies in Minnesota and North Dakota. No one else has been charged in Engst’s death.