BILLINGS (AP) — Attorneys for a Colorado man accused of murdering a teacher in Montana’s oil patch asked a judge Friday to order an accomplice to appear as a defense witness when the case goes to trial.

Michael Keith Spell, 25, could face life in prison if convicted in the killing.

His accomplice, Lester Van Waters Jr., pleaded guilty last year to deliberate homicide by accountability under a plea deal with prosecutors that spared him the death penalty.

Prosecutors say Spell choked or otherwise asphyxiated Sherry Arnold, 43, during an attempted abduction.

But Spell’s attorneys said in documents filed Friday that statements by Waters during his plea hearing show Spell did not intend to injure Arnold.

The Sidney High School math teacher and mother of two was killed just blocks from her house on Jan. 7, 2012. Her body was found more than two months later, buried in a shallow grave in a rural area of neighboring North Dakota.

Waters and Spell, both of Parachute, Colorado, had gone to the northeast Montana town of Sidney looking for work in the Bakken oil patch.

Waters said during his change-of-plea hearing that the pair consumed large amounts of cocaine during their drive from Colorado and were in Sidney looking for a prostitute to have sex with when they saw Arnold, who was out on her morning run.

“The plan was she would go voluntarily with them and she would not be taken against her will,” Spell’s attorneys, Al Avignone and Lisa Banick, wrote in their motion seeking to have Waters appear at Spell’s trial.

Richland County Attorney Mike Weber did not immediately respond to a request for comment. He previously declined to discuss the case outside the courtroom.

Waters’ attorney, Gregory Jackson, also did not immediately respond to a request for comment. Under his June 2013 plea agreement, Waters agreed to testify on the state’s behalf if requested.

Avignone said it was unusual for both the prosecution and the defense to want a co-defendant to testify.

A three-week trial is set for Nov. 17 in Glendive, after being delayed for months while Spell underwent a mental evaluation. Psychiatrists say Spell has a low IQ, can barely read and doesn’t understand some basic life tasks.

Those mental disabilities prompted prosecutors in May to drop their pursuit of the death penalty in his case. A 2002 U.S. Supreme Court ruling banned executions of mentally disabled people as cruel and unusual punishment.

But State District Judge Richard Simonton rejected attempts by Spell’s attorneys to have him declared incompetent. That would have let Spell avoid trial and made him eligible for eventual release.

Avignone said he plans to file a petition with the Montana Supreme Court seeking to overturn Simonton’s competency ruling.