It is likely, but not guaranteed, that when Aurora movie theater shooting suspect James Holmes appears in court Monday, the judge overseeing the case will allow Holmes to change his plea to not guilty by reason of insanity.

Under Colorado law, insanity pleas must be entered at arraignment — a hearing in Holmes’ case that took place in March. At that time, a judge entered a not guilty plea to the charges on Holmes’ behalf after his attorneys refused to enter a plea.

Insanity pleas can only be entered later if a defendant shows “good cause” for the change, according to the law. The law doesn’t spell out what “good cause” means.

“Ultimately … the question of good cause is one addressed to the sound discretion of the trial judge,” the Colorado Supreme Court ruled in a 1980 case.

However, other state Supreme Court rulings make clear that judges should err on the side of allowing the change.

In one case, the state’s highest court ruled that a trial judge went too far in requiring a defendant to submit to a mental-health evaluation just to show good cause. In another case, the state Supreme Court ruled that a plea change should have been allowed in a case where the defense attorney learned about documentation of mental illness just prior to trial.

In cases where the state Supreme Court has upheld decisions to deny plea changes, it is typically because the change was requested too close to the trial date or because defense attorneys provided flimsy reasons for the change.

“In our view,” the state Supreme Court ruled in a 1975 case, “good cause is shown when it is demonstrated that fairness and justice are best subserved by permitting the additional plea.”

For that reason, legal experts expect Judge Carlos Samour to allow Holmes to change his plea to not guilty by reason of insanity. Holmes’ trial date is still months away. And, the experts predict, Holmes’ attorneys will likely say they have only recently completed their own psychiatric evaluations of Holmes.

There’s another reason to allow the change, said Denver defense attorney Dan Recht, who is not involved in the case but has been following developments in it. If Samour denies Holmes’ efforts to enter an insanity plea, a lengthy appeal will likely follow — in the middle of the murder case.

“It’s a foregone conclusion that the court will allow Holmes to change his plea to not guilty by reason of insanity,” Recht predicted.

Holmes is charged with 166 counts of murder, attempted murder and other offenses in connection with the attack at the Century Aurora 16 movie theater. Twelve people were shot to death in the attack, and another 58 were wounded by gunfire.

If Holmes is allowed to plead insanity, Samour will order him to undergo an independent mental-health evaluation.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold