Prosecutors are expected to call on doctors from the Montana state mental hospital Tuesday to bolster claims that a Colorado man is fit to stand trial in the killing of a teacher in the heart of the Bakken oil patch.

Defense experts testified this week that 24-year-old Michael Keith Spell is prone to distort the past and has the intelligence of an 11-year-old, leaving him unable to understand the case against him.

But their testimony also revealed that doctors at Montana State Hospital suspected 24-year-old Michael Keith Spell was "faking it" when he could not answer some questions during a recent mental fitness evaluation.

Psychiatrist Virginia Hill and psychologist Timothy Casey evaluated Spell during a two-month stay at the hospital in Warm Springs. Richland County Attorney Mike Weber said he plans to call them to the stand Tuesday as a competency hearing for Spell continues in Sidney.

Judge Richard Simonton will have to reconcile the competing claims to determine if Spell is incompetent to stand trial because of mental disability, as his lawyers contend.

Spell is charged with the attempted kidnapping and murder of 43-year-old Sherry Arnold, who disappeared in January 2012 after going out for a morning jog in her hometown of Sidney. Her body was found more than two months later, buried in a shallow grave in a rural area of neighboring North Dakota.

Spell could face the death sentence if convicted. But if Simonton agrees with the defense claims, Spell could avoid trial and be sent to a state institution, where he could become eligible for eventual release.

A co-defendant has pleaded guilty under a deal with prosecutors that called for him to testify against Spell.

The case has unfolded as crime rates spiked over the past several years in eastern Montana and neighboring parts of North Dakota, where an oil boom has transformed once-quiet agricultural communities. The killing of Arnold — a Sidney High School math teacher widely beloved in the community — stood out for its violent, random nature.

Testifying for the defense, Craig Beaver, a Boise, Idaho-based neuropsychologist, said Spell was prone to distort past events, which would effectively hobble any criminal defense he might mount.

Beaver added that he was able to document evidence of Spell's mental shortcomings dating to when the defendant was just 5 years old, which Beaver said undercut any claim that the defendant was exaggerating his condition just to avoid trial.

Spell was declared incompetent to proceed by courts in Colorado during a 2010 drug case and a 2007 case when he was a juvenile.

"Everyone that has evaluated Mr. Michael Spell, up until the Montana State Hospital, has found that he had intellectual limitations," Beaver said.

Court documents, including law enforcement affidavits and testimony from Spell's accomplice say the defendants arrived in Montana after a drug-fueled drive from Parachute, Colo., and spotted Arnold along a Sidney street. Arnold died after Spell choked or otherwise asphyxiated her during an attempted abduction, according to the documents.

Spell implicated co-defendant Lester Van Waters Jr. as the killer in an FBI interview after his arrest.

His attorneys have not denied Spell's involvement in the events leading up to Arnold's death, but say there is no "conclusive evidence" he was the one who killed her.