STURGIS, S.D. (Rapid City Journal) — Attorneys say a South Dakota teenager plans to plead guilty to manslaughter in the death of a 16-year-old Wyoming girl whose body was found in his basement last fall.

The 17-year-old defendant originally was charged as an adult with alternative counts of first- and second-degree murder in the killing of Shayna Ritthaler of Upton, Wyoming.

The prosecutor tells the Rapid City Journal the boy is expected to plead guilty to manslaughter on Thursday.

He originally pleaded not guilty and not guilty by reason of insanity.

The prosecutor and the teen's attorney have agreed to ask the judge for a 55-year sentence, but the judge does not have to agree to their recommendation.

The prosecutor has said the suspect shot Ritthaler after an argument.

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