Does a Colorado law violate the Constitution by requiring defendants to cooperate in court-ordered mental evaluations when they plead not guilty by reason of insanity?

That’s a question an Arapahoe County District Court judge must answer before deciding whether to accept such a plea from Aurora theater shooting suspect James Holmes.

Holmes attorney Kristen Nelson on Thursday told Judge Carlos Samour that the state’s insanity-plea rule is unconstitutional because it would bar testimony from mental health experts, who could offer mitigating factors, during the sentencing phase of Holmes’ trial. Prosecutors are seeking the death penalty against the 24-year-old charged with 166 counts of murder, attempted murder and other crimes in connection with the July 20 shooting at the Century Aurora 16 movie theater. Twelve people were killed and 58 more were wounded by gunfire.

“You can’t place limitations on the number of mitigating factors a sentencer can hear,” Nelson said during an hour-long hearing in which Samour made no ruling. Death-penalty defendants should be able to present expert testimony at sentencing regardless of whether they are deemed cooperative during a sanity evaluation, she said.

Holmes’ attorneys want Samour to decide on their constitutional questions by May 31, when he will be advised of the conditions of pleading not guilty by reason of insanity. Samour will decide whether to accept that plea after Holmes is advised.

Senior Deputy District Attorney Rich Orman told the judge that the state’s insanity-plea laws are fair. If a defendant won’t cooperate during a mental health evaluation, he said, a sentencer will have no way of knowing whether the testimony at sentencing is legitimate. Colorado appeals courts have upheld the requirements, he said.

If Holmes were found to be uncooperative during his future evaluation, Orman added, there would be a hearing to determine whether he could call certain experts during his sentencing.

But Nelson said, “the entire statute is a problem because we don’t know how to advise him.”

Holmes’ formal request earlier this month to change his plea to not guilty by reason of insanity triggered the legal fight over Colorado’s laws governing such pleas. His attorneys filed a series of motions challenging the constitutionality of a number of insanity-plea rules, especially as they apply to death-penalty cases.

The statute, they say, is both unconstitutional on its face and as it applies to Holmes.

Sadie Gurman: 303-954-1661, sgurman@denverpost.com or twitter.com/sgurman