Lawyers defending Colorado movie theater shooting suspect James Holmes Thursday questioned the very constitutionality of Colorado's insanity defense statute.

Holmes, who officially pleaded "not guilt by reason of insanity" earlier this month, now faces court-ordered mental evaluations, during which he is expected to admit to last summer's shooting at a midnight showing of a Batman movie that left 12 people dead and 58 wounded.

But public defense attorneys said such a confession would be a violation of the protection against "self-incrimination," as stipulated in the Fifth Amendment to the US Constitution.

Additionally, Colorado's insanity-plea rule is unconstitutional because it might stop testimony from mental health experts who could offer mitigating factors during the sentencing phase of Holmes' trial, according to public defender Kristen Nelson.

Holmes' defense team called the entire insanity-plea statute a problem "because we don't know how to advise him," Nelson said.

District Court Judge Carlos Samour will decide on these constitutional questions by May 31, when Holmes will be advised of the consequences of pleading not guilty by reason of insanity. Samour will then decide whether to accept that plea, which he is expected to do.

"Their goal is to avoid capital punishment (the death penalty), and this is just one more issue," said Craig Silverman, a former Denver prosecutor who successfully prosecuted Colorado's last death penalty case.

"If the judge can conceivably find that part of the law is unconstitutional, then we have a big problem," Silverman said, "How can they put someone to death under those circumstances?"

Prosecutors argued Thursday that Colorado's insanity laws are fair. And, if a defendant (Holmes) "does't cooperate" during a mental health evaluation, deputy district attorney Rich Orman said, a "sentencer will have no way of knowing whether the testimony at sentencing is legitimate."

Holmes' attorneys have recently filed a series of motions challenging the constitutionality of a number of insanity-plea rules, especially as they apply to death penalty cases.

In Colorado, the burden of proof lies with the prosecution to determine whether Holmes was insane at the precise time of the act, according to Silverman.