HELENA, Mont. (AP) — The Montana Supreme Court ruled unanimously that the man who helped kill a Montana teacher in 2012 was mentally competent when he pleaded guilty.

The Independent Record reports Michael Spell was sentenced to 100 years in the Montana State prison in May 2015 after he pleaded guilty to deliberate homicide in the death of Sherry Arnold.

A review by the court of expert witness testimony, evidence and assessments made by medical professionals turned up insufficient reason to support any part of Spell's appeal that questioned multiple aspects of how the District Court of the Seventh Judicial District assessed his mental competence.

Arnold went jogging In January 2012 and did not return home. Spell and another man were arrested a week later. Arnold's body was later found buried in North Dakota.

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Information from: Independent Record, http://www.helenair.com