BILLINGS — A Colorado man charged with killing an Eastern Montana teacher has been returned to jail following a lengthy evaluation to see if he’s fit for trial.

The Richland County Sheriff’s Office said Friday that Michael Spell had returned to the county detention center from the Montana State Hospital in Warm Springs. He had been undergoing tests to determine his competency since November.

Prosecutors are seeking the death penalty for Spell in the killing of Sherry Arnold.

State District Judge Richard Simonton has ordered doctors at the state psychiatric hospital to complete Spell’s competency report and deliver it to defense lawyers by Jan. 31.

One of Spell’s attorneys, Al Avignone, said he anticipates seeking a March fitness hearing that could last several days. He said as many as seven witnesses could be called to testify on Spell’s mental state.

Authorities say Spell strangled or asphyxiated the 43-year-old Sidney High School teacher when he attempted to abduct her as she was jogging on Jan. 7, 2012. Her body was found more than two months later buried in a shallow grave in a rural area near Williston, N.D.

Attorneys for the 24-year-old defendant from Parachute, Colo., say he has mental disabilities that render him unable to understand the case against him or assist in his defense. If that argument prevails, the case could end up being dismissed, with Spell institutionalized.

Spell has said in court that he cannot read. Avignone claims the defendant since the age of 15 has consistently scored below 75 on IQ tests, a cutoff intelligence level considered a central indicator of mental disability.

Co-defendant Lester Van Waters, Jr. pleaded guilty last year under a deal with prosecutors that would allow him to avoid the death sentence in exchange for helping in the case against Spell. He’s awaiting sentencing.