Batman cinema massacre gunman James Holmes wants to plead not guilty through insanity, a move seen as his best chance of avoiding the death penalty.
Prosecutors are seeking the death penalty. They say Holmes, a former neuroscience graduate student, spent months acquiring weapons and ammunition, scouting a cinema in the Denver suburb of Aurora and booby-trapping his apartment.
Then on July 20, dressed in a police-style helmet and body armour he opened fire during a packed midnight showing of The Dark Knight Rises. Twelve people died and 70 were injured.
No motive has emerged in nearly 10 months of hearings, but Holmes' lawyers have repeatedly said their client is mentally ill. He was being treated by a psychiatrist before the attack.
A judge entered a standard not guilty plea on Holmes' behalf in March, and he needs court permission to change it. Holmes' lawyers have held off on changing his plea until now, fearing a wrinkle in the law could cripple their ability to raise his mental health as a mitigating factor during the sentencing phase.
Two judges have refused to rule on the constitutionality of the law, saying their objections were hypothetical because Holmes had not pleaded insanity. The defence had little choice but to have Holmes enter the plea and then challenge the law.
Holmes' lawyers announced last week that Holmes would ask to change his plea at the hearing. The insanity plea carries risks for both sides. Holmes will have to submit to a mental evaluation by state-employed doctors, and prosecutors could use the findings against him.
"It's literally a life-and-death situation with the government seeking to execute him and the government, the same government, evaluating him with regard to whether he was sane or insane at the time he was in that movie theatre," said lawyer Dan Recht, a past president of the Colorado Criminal Defence Bar.
Prosecutors must convince jurors beyond a reasonable doubt that Holmes was sane. If they fail, state law requires the jury to find him not guilty by reason of insanity.
If acquitted, Holmes would be committed to the state mental hospital indefinitely. The mental evaluation could take weeks or months. Evaluators will interview Holmes, his friends and family, and if Holmes permits it, they'll also speak to mental health professionals who treated him in the past.