Aurora, Colo., theater gunman James Holmes wants to change his plea to not guilty by reason of insanity, his lawyers said Tuesday.

Defense attorneys said in a court filing in Denver that they will formally request the change of plea at a May 13 hearing, the Associated Press reports.

The insanity plea was expected given the overwhelming evidence against Holmes, who opened fire July 20 in a packed theater in the Denver suburb of Aurora during a midnight screening of the Batman film "The Dark Knight Rises." Twelve people were killed and 70 wounded.

But his lawyers delayed entering an insanity plea for weeks, saying Colorado's insanity and death penalty laws overlapped in a way that could severely — and unconstitutionally — hamper his defense if he did plead insanity.

The defense has asked both judges who have presided over the case to rule on the constitutionality of the laws. Both judges refused, saying the question was speculative because Holmes hadn't entered an insanity plea. That left his lawyers with no choice but to enter the insanity plea, then seek a ruling on the constitutionality question.

Holmes, 25, is charged with multiple counts of murder and attempted murder.

A judge in the case previously entered a standard not guilty plea for him. If a judge accepts the new plea, Holmes would be sent to a mental hospital, where doctors would determine whether he was insane at the time of the shootings.

If the doctors do determine that Holmes was insane, a jury could still find him guilty.

Colorado law defines insanity as the inability to distinguish right from wrong, caused by a diseased or defective mind. The law specifically excludes depravity, "moral obliquity" or passion caused by anger or hatred from being considered insanity.

Prosecutors, who are seeking the death penalty, declined to comment Tuesday.