SIDNEY, Mont. (AP) – One of the men accused of killing an eastern Montana high school teacher has made a deal with prosecutors that would spare him the death penalty in exchange for testifying against his co-defendant.

Lester Van Waters Jr., of Colorado, has agreed to plead guilty to deliberate homicide by accountability in the January 2012 slaying of Sidney High School math teacher Sherry Arnold, according to the plea agreement filed in state court Monday.

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Prosecutors have agreed to drop an attempted kidnapping charge and will recommend a sentence of 100 years in prison with 20 years suspended, instead of the death penalty.

Waters also has agreed to cooperate with the state’s prosecution of co-defendant Michael Spell.

A change-of-plea hearing has been set for Tuesday in which District Judge Richard Simonton will decide whether to accept the agreement.

Waters and Spell are accused of abducting Arnold while she was out for a morning jog on Jan. 7, 2012. The two men are from Parachute, Colo., and had arrived in the region looking for work in the oil fields.

The men at some point either strangled her or held her face in mud or water until she died, prosecutors said. Her body was found about two months later buried in a shallow grave in a field near Williston, N.D., about 50 miles from Sidney.

Waters and Spell were arrested about a week after her disappearance. Waters was 48 at the time and Spell was 22.

Spell has pleaded not guilty to the charges. His defense team has asked Simonton to rule out a potential death sentence because Spell is mentally disabled.

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Spell is illiterate and his father has said he has less education than a kindergartner.

A 2002 U.S. Supreme Court ruling banned executions of the mentally disabled, saying it violated the constitutional prohibition against cruel and unusual punishment.

Spell previously acknowledged his role in what an affidavit described as the crack-fueled abduction and killing of Arnold.

His attorneys want to exclude those statements from trial, saying his mental disabilities made Spell unable to understand that he was waiving his constitutional rights in speaking to investigators.

His attorneys also are asking that his Jan. 6 trial be moved to Bozeman because they believe Richland County jurors would be biased because of the publicity the case has received, and they are asking prosecutors to turn over any agreements and promises they made to Waters for his testimony.

Simonton has not ruled on the motions.

Waters had been scheduled for a Nov. 4 trial after initially pleading not guilty to the charges.

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