BILLINGS, Mont. (AP) — Prosecutors in eastern Montana asked a state judge Wednesday to deny a defense request to suppress an alleged confession by the suspect in a high-profile murder case.

Michael Keith Spell, 25, of Parachute, Colorado, is accused of killing 43-year-old Sidney High School math teacher Sherry Arnold during an attempted random abduction in the Bakken oil patch. Her body was found more than two months later in a shallow grave in North Dakota.

Spell allegedly confessed to his involvement in the crime six days after Arnold disappeared, during an interrogation by FBI agents in the hours following his arrest by a SWAT team in South Dakota. Because Spell is mentally disabled, his attorneys say he was not capable of voluntarily waiving his rights to remain silent and have an attorney present.

But Deputy Richland County Attorney T.R. Halvorson wrote in a court brief that video of the interview shows Spell made his statements voluntarily.

State District Judge Richard Simonton has scheduled an Oct. 1 hearing on the matter.

“The court has the video by (Special Agent) George Doberstein. The court has the testimony of SA Doberstein. The court can observe directly and for itself whether there was coercion, lawlessness, or undue advantage taken of Michael Spell’s condition,” Halvorson wrote. “The statement by Michael Spell was voluntary, and the video shows it.”

Spell attorney Al Avignone said the defense was not alleging that any kind of force or other improper actions were taken against Spell — only that his disability rendered him incapable of consenting to an interview.

“He does not understand his Constitutional rights and can’t voluntarily waive his rights,” Avignone said.

Prosecutors dropped their pursuit of the death penalty in the case after experts testified Spell is mildly mental disabled. A 2002 U.S. Supreme Court ruling prohibits executions of the mentally disabled as cruel and unusual punishment.

The defense has not disputed that Spell was involved in the events leading up to Arnold’s disappearance but contends there’s no definitive proof he killed her.

A second defendant, Lester Van Waters Jr., also of Parachute, has pleaded guilty to deliberate homicide by accountability in a deal with prosecutors.

Spell told the agents that he and Waters had arrived in Sidney looking for work in the Bakken oil fields along the Montana-North Dakota border, according to excerpts of Spell’s interrogation cited by prosecutors. After smoking large amounts of crack cocaine, Waters said he wanted to kidnap and kill a woman.

After the first woman they hoped to target, at a public laundry, left before they could carry out their plan, Spell said the pair saw Arnold. Spell said he grabbed her and dragged her back to their vehicle, where Waters killed her, according to court documents.

Waters has implicated Spell as the killer.