text: A mentally disabled Colorado man was sentenced to 100 years in prison Friday for the murder of a Montana teacher whose death highlighted the downsides of an oil boom that's sweeping across the remote Northern Plains, bringing thousands of newcomers to the area. Michael Keith Spell, 25, of Parachute, Colorado, was sentenced following a hearing before state District Judge Richard Simonton in Sidney. Spell pleaded guilty in October to killing Sherry Arnold, 43, after attempting to abduct the popular math teacher as she was jogging near her home in 2012. Arnold's body was found months later buried in a shallow grave in a rural area near Williston, North Dakota. Co-defendant Lester Van Waters Jr. was sentenced in December to 80 years in prison on a charge of deliberate homicide by accountability. Sentenced to die behind bars: Michael Keith Spell, 25, sits in state District Court in Sidney, Mont, Friday April 17, 2015, before being sentenced to 100 years prison for the 2012 murder of a 43-year-old teacher in the booming Bakken oil patch of Montana . Murdered at random: Sherry Arnold, a popular maths teacher from the small town of Sidney, Montana, was on a morning jog on January 7 when she disappeared. She was pulled into a car by Spell and his friend, strangled to death, and then buried 50 miles away in North Dakota . Defense attorneys had asked that Spell be placed into custody of state health officials for placement in an institution for the mentally disabled. They claimed he was 'easily confused and displays the intelligence of an 11-year-old'. They said Spell's mental problems made him unable to conform to the law, making him eligible for commitment to the Montana Department of Health and Human Services. In the days before Arnold's killing, Spell and Waters traveled to Sidney from Colorado, using crack cocaine throughout their journey, according to authorities and the men's previous testimony. The defendants came to the region looking for work in the booming Bakken oil patch. During their trip, Waters allegedly told Spell that using crack "brought the devil out in him" and began talking about kidnapping and killing a woman, according to an affidavit filed by prosecutors. Spell's attorneys alleged Waters threatened to kill Spell with a utility razor unless he went along with the kidnapping plan. After the pair spotted Arnold along a Sidney street, Spell tried to grab her, leading to a struggle in which Arnold was choked or otherwise asphyxiated, authorities said. Co-accused: Lester Van Waters (left) was sentenced to 80 years in December.  He and Spell (right-in 2012) were under the influence of crack cocaine when they kidnapped and murder Mrs Arnold . Killed: Michael Spell told investigators he pulled Sherry Arnold into a car and Waters choked her to death by before they buried her in a shallow grave on a farmstead near Williston . Spell said during an October change-of-plea hearing that he was unsure if he or Waters had killed Arnold. Arnold's body was found months after her disappearance in a shallow grave in a rural area near Williston, North Dakota. For Sidney residents, Arnold's death offered a horrifying illustration of the social upheaval caused by an energy boom that has turned the once-sleepy town into an oil patch hub. Crime has spiked in the Bakken region of Montana and North Dakota over the past several years as traffickers of methamphetamine and other drugs seek to profit off oil workers flush with cash, according to law enforcement officials. Spell was spared a potential death sentence after state health officials agreed with the defense that he was mentally disabled. Guilty: In this February 2012 photo, Michael Keith Spell, appears at a hearing in the Williams County Courthouse in Williston. Defense attorneys wanted Spell sentenced to an institution for the mentally disabled . Dearly missed: Rhonda Whited-Rupp holds a picture of her sister, Sherry Arnold, seen in a cowboy hat, and Arnold's family. Michael Keith Spell was sentenced to 100 years prison Friday for the murder of Mrs Arnold . But Simonton in May rejected arguments from the defense that Spell's history of low IQ scores, his difficulty reading and other mental problems rendered him incompetent to stand trial. Prosecutors recommended 100 years in prison and thus became Spell's sentence Friday. Defense attorneys Al Avignone and Lisa Banick said Friday's judgment will be appealed based on their continued belief that he was not fit for trial. If the state Supreme Court agrees, Spell would be committed to a state mental institution, Avignone said.
target: Sherry Arnold, a 44-year-old math teacher from Sidney, Montana, was on a morning jog on January 7, 2012, when she was abducted .
  Michael Keith Spell, 25, of parachute, Colorado, confessed at the time to pulling her into a car while his friend, Lester Van Walters Jr, strangled her .
  Arnold was then buried 50 miles away near Williston, North Dakota .
  Defense experts said Spell did not understand the case against and was mentally unfit to stand trail .
  Prosecutors agreed he was mentally ill but said he could stand trial, recommending 100 years prison .