James Holmes, Aurora theater shooting suspect, sits in the courtroom during his arraignment in Centennial, Colo., on Tuesday, March 12, 2013.
The mental evaluation for Colorado theater shooting suspect and Rancho Penasquitos resident could take weeks or even months if the judge allows a plea of not guilty by reason of insanity.
James Holmes faces 166 counts of murder, attempted murder and other offenses in connection with the July 20 shooting in an Aurora, Colorado movie theater that left 12 dead and 58 wounded.
His mother, Arlene Holmes, was in court Monday when his attorneys told a judge Holmes wants to change his plea to not guilty by reason of insanity.
Attorney Daniel King made the request in court, saying the defense now has a diagnosis for James Holmes, though he didn't specify what it was.
Holmes, with bushy hair and beard, didn't speak during the hearing after entering the courtroom with his eyes downcast.
Before deciding whether to accept a new plea, Judge Carlos Samour said, he would consider arguments about constitutional questions the defense has raised about Colorado's insanity and death penalty laws.
He isn't expected to announce his decision until May 31, when another hearing is scheduled.
Prosecutors are seeking the death penalty. They say Holmes, a former neuroscience graduate student, spent months acquiring weapons and ammunition, scouting a theater in the Denver suburb of Aurora and booby-trapping his apartment.
Then on July 20, dressed in a police-style helmet and body armor, he opened fire during a packed midnight showing of "The Dark Knight Rises," prosecutors say.
Holmes, a Westview High School graduate, attended UC Riverside where he graduated a BS in neuroscience in 2010. He then went to Colorado where he was pursuing his graduate degree.
While in San Diego, James Holmes lived with his parents Robert and Arlene Holmes on Sparren Avenue in Rancho Penasquitos.
Arlene Holmes, a registered nurse, works with Tri-City in Oceanside. The defendant's father, Robert Holmes, is a software engineer who lists his employer as a Carmel Valley company.
No motive has emerged in nearly 10 months of hearings, but Holmes' attorneys have repeatedly said their client is mentally ill. He was being treated by a psychiatrist before the attack.
A not guilty by reason of insanity plea is widely seen as Holmes' best hope -- perhaps his only hope -- of avoiding the death penalty.
But his lawyers have held off 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.
The insanity plea carries risks for both sides. Holmes will have to submit to the 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 theater," said attorney Dan Recht, a past president of the Colorado Criminal Defense 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 judge entered a standard not guilty plea on Holmes' behalf in March, and he needs court permission to change it.
The 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.