HELENA (AP) — A mentally disabled Colorado man accused of killing a Montana teacher and burying her body is asking the state Supreme Court to reverse a judge’s ruling that he is fit to stand trial.

An attorney for Michael Spell, 25, filed a petition late Friday asking the justices to rule that District Judge Richard Simonton was wrong when he concluded in May that Spell could assist in his own defense.

Spell faces a complicated murder trial that will include more than 130 witnesses and numerous exhibits, attorney Al Avignone said in the filing.

The defendant is “intellectually disabled, illiterate and has significant deficits in understanding language and articulating thoughts,” Avignone wrote.

Spell reads at a second-grade level and cannot write much beyond his own name, the attorney said. Psychiatrists say Spell has a low IQ and doesn’t understand some basic life tasks.

“Michael must be able to make decisions as to his case and defense based on his own understanding of the charges, his own knowledge of the facts, his own assessment of his particular situation and his own evaluation of his lawyer’s advice on tactics and strategy. Michael cannot do this,” Avignone wrote.

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.

Spell is charged with the attempted kidnapping and deliberate homicide in the killing of Sidney High School teacher Sherry Arnold, 43, who disappeared while on a morning jog in January 2012. Her body was found more than two months later in a shallow grave in nearby North Dakota at the center of the Bakken oil boom.

Spell and Lester Van Waters were arrested. Van Waters pleaded guilty in August 2013 to deliberate homicide by accountability in a deal with prosecutors. Under the agreement, he would be spared the death penalty and receive 100 years in prison in exchange for testifying against Spell.

Spell could face a maximum possible sentence of life in prison if convicted. A trial is set for Nov. 17.

Simonton, the judge, had sided with the conclusions of Dr. Virginia Hill, a psychiatrist from the state mental hospital in Warm Springs who evaluated Spell. She said Spell had matured mentally since being ruled mentally incompetent in a previous legal proceeding in Colorado and he had benefited from being off drugs since his arrest in Arnold’s death.

Avignone said Hill has no expertise in intellectual disabilities, didn’t spend enough time with Spell and inappropriately evaluated him at the Warm Springs facility, when he should have been evaluated in his typical community setting.

The judge instead should have relied on the expertise of two defense witnesses who found Spell had a very limited capacity to understand the proceedings against him, Avignone said.