A Warwick, N.D., man plans to plead guilty to kidnapping and murder charges related to a body found more than three years ago in the Sheyenne River.

A plea agreement filed Wednesday in Fargo's federal court said prosecutors plan to recommend Billy Joe Herman be sentenced to life in prison. A trial date, which was rescheduled four times, has been cancelled.

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The indictment reveals few details but said Herman kidnapped 36-year-old Amanda Jean Stach Engst, "violently bludgeoning her with his fist and shod feet" and strangling her with a cord around Oct. 12, 2015. Engst's body was found Feb. 4, 2016, in the Sheyenne River south of Warwick, N.D.

Herman with charged in federal court with murder, kidnapping and assault with the intent to commit murder in June 2018. The crimes hold a maximum penalty of life in prison.

Herman's wife, 39-year-old Crystal Marie Herman, pleaded guilty in January 2018 in Eddy County to charges of accomplice to murder. She was sentenced to 20 years in prison, although the maximum punishment could have been life.

An affidavit for Crystal Herman's arrest said she opened a car door near the east end of Battle Lake in Eddy County so her husband could strangle Engst outside the vehicle. She allegedly cleared items from the trunk to make room for Engst's body. The affidavit said Crystal Herman then watched her husband wrap Engst's body in a tarp and place her in the trunk before driving to the Sheyenne River on the Spirit Lake Indian Reservation. She held a flashlight and watched as Billy Joe Herman again beat Engst, rewrapped her into the tarp and threw her body into the river, the affidavit said.

There are several charges against the couple for robberies in Minnesota and North Dakota around the time of Engst's disappearance. A court document said they were found in Engst's car and arrested related to the robberies about a week before her body was found.

Engst went missing just two months after Carla Jovon Yellowbird's body was found alongside a road on the Spirit Lake Indian Reservation. Three men were sentenced for Yellowbird's death.

Engst grew up in Breckenridge, Minn., and had three children, her obituary said. She had a CNA certificate and worked at Red River Human Services, where her obituary said she found joy in working with people with special needs.

A sentencing date has not yet been determined by the federal court.