By Laura Zuckerman
April 17 (Reuters) - A man who admitted killing a Montana teacher during a cocaine frenzy was sentenced to 100 years in prison by a state judge on Friday in a case that authorities said underscored a crime wave that accompanied a regional oil boom.
Michael Spell, 25, of Parachute, Colorado, pleaded guilty in October to deliberate homicide in the strangling death of math instructor Sherry Arnold, legal documents showed. Under a deal with prosecutors, an attempted kidnapping charge was dropped.
The agreement came after several court hearings that sought to determine Spell's competence, with defense attorneys claiming he was unfit to stand trial because of mental deficiencies.
Arnold, 43, vanished in January 2012 while on a predawn run in her rural hometown of Sidney, where at the time authorities were noting a sharp increase in population and crime tied to an oil boom spanning northeastern Montana and northwestern North Dakota.
Spell later told police he and Lester Waters, a friend from Parachute, had smoked crack cocaine while driving through Sidney to oilfield jobs in Williston, North Dakota, when Arnold jogged by and Waters ordered him to pull her into their car.
Spell told investigators Waters "choked her out" in the back seat, but prosecutors accused Spell of strangling the teacher.
Arnold "lay dead inside the vehicle and under a blanket" while the men drove to Williston, where they disposed of her clothing in a dumpster and bought a shovel to bury the body in a shallow grave outside town, a Montana prosecutor said in a sworn statement.
Spell apologized for his actions during Friday's sentencing hearing before Judge Richard Simonton in Sidney, a court official said. His defense attorney did not immediately respond to a request for comment.
Waters was sentenced by a Montana judge in December to 80 years in prison for his role in Arnold's death, state Department of Corrections records show. (Reporting by Laura Zuckerman in Salmon, Idaho; Editing by Daniel Wallis and Eric Beech)