CENTENNIAL, Colo. - Lawyers for Colorado theatre shooting suspect James Holmes formally told a judge on Monday that he wants to change his plea to not guilty by reason of insanity after outside experts diagnosed his mental illness.
The attorneys, however, did not specify the diagnosis. Judge Carlos Samour Jr. indicated he would not decide whether to approve the new plea until the end of the month.
A judge entered a standard not guilty plea on Holmes' behalf in March, and he needs court permission to change it.
Holmes is charged with more than 160 counts of murder and attempted murder in the July 20 shootings that left 12 people dead and 70 injured.
He appeared at Monday's hearing with bushy brown hair and a full beard. He entered the courtroom with eyes downcast and didn't speak.
Prosecutors are seeking the death penalty, and the insanity plea is widely seen as Holmes' best chance to avoid execution.
No motive has emerged in nearly 10 months of hearings, but Holmes' attorneys have repeatedly said he is mentally ill. He was being treated by a psychiatrist before the attack, but the reason for the treatment hasn't been disclosed.
Before Samour decides on the change of plea, he must rule on questions raised by the defence about the constitutionality of Colorado's insanity and death penalty laws. Holmes' lawyers have argued that a wrinkle in the laws could cripple their ability to raise his mental health as a mitigating factor during the sentencing phase.
The move by the defence to change Holmes' plea was a significant step as the case slowly creeps toward a trial or possible plea agreement.
With Holmes' life at stake, even the smallest details take on more importance. Samour even notified lawyers in court on Monday that he was removing two commas from a document.
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 attorney Dan Recht, a past president of the Colorado Criminal Defence Bar.
Among the risks for prosecutors: They must convince jurors beyond a reasonable doubt that Holmes was sane. If they don't, state law requires the jury to find him not guilty by reason of insanity.
"That's a significant burden on the prosecution," Recht said.
If acquitted, Holmes would be committed to the state mental hospital indefinitely.
A state mental evaluation could take weeks or months. Evaluators would interview Holmes, his friends and family, and if Holmes permits it, they'll also speak with mental health professionals who treated him in the past, said Dr. Howard Zonana, a professor of psychiatry and adjunct professor of law at Yale University.
Evaluators may give Holmes standardized personality tests and compare his results to those of people with documented mental illness. They will also look for any physical brain problems.
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