BILLINGS, Mont. -

Attorneys for a Colorado man charged in the murder of an eastern Montana teacher say the defendant was diagnosed with mental disability following a recent evaluation at Montana State Hospital.
   
Attorneys for 24-year-old Michael Keith Spell argue that their client's disability makes him unfit to be tried in the January 2012 killing of 43-year-old Sherry Arnold of Sidney.
   
On Thursday, Spell's attorneys said in a court filing that a Jan. 29 report shows doctors at the state hospital diagnosed him as disabled. The filing did not disclose if the doctors found him incompetent.
   
But Spell's attorneys wrote that the doctors' opinions regarding Spell's fitness to proceed were "unfounded and not reliable" - suggesting they run counter to defense arguments.
   
A two-day competency hearing is scheduled for next week.