Colorado theater shooter James Holmes appeared clean shaven and with a neat haircut as lawyers made their final motions before Monday's opening of the trial that will determine if he'll be executed, spend his life in prison, or be committed to a mental institution as criminally insane.

His clown-like red hair grew out long ago, and the bushy beard he wore before the trial was gone, too. Discreetly, so that others can't see, Holmes was restrained by a harness under his blue shirt and khaki pants, tethered to the floor of the courtroom where his trial is expected to take months.

His fate depends on what the jury learns about his mental state three years ago, when he slipped into a midnight Batman premiere, unleashed tear gas and marched up and down the aisles, firing at people who tried to flee.

Holmes acknowledges killing 12 people and wounding 70 more inside the packed theater, but has pleaded not guilty by reason of insanity.

Robert and Arlene Holmes, who waited with parents of his victims Monday in a drizzly rain before entering the courthouse, have pleaded for his life, calling their son a "human being gripped by a severe mental illness."

Unlike most other states, Colorado puts the burden on prosecutors, who must convince jurors beyond a reasonable doubt that Holmes was sane.

Colorado has already spent millions seeking that verdict, managing an outsized number of victims, witnesses and more than 85,000 pages of evidence.

Experts say Holmes faces long odds. Insanity defenses are successful in only 25 percent of felony trials nationally, even less so in homicides.

"Lay people tend to think of people with mental illness as extremely dangerous, and that also influences jurors, especially if someone has killed someone," said Christopher Slobogin, who teaches law and psychiatry at Vanderbilt Law School. "Usually there's evidence of intent and planning that seems to be counterintuitive to the lay view of mental illness."

Winning a trial on mental-health grounds is rare, but then again, so are jury trials for mass shooters. Most are killed by police, kill themselves or plead guilty.

A review of 160 mass shootings found killers went to trial 74 times, and just three were found insane, according to Grant Duwe, a Minnesota corrections official who wrote the book "Mass Murder in the United States: A History."

Just one won a mental-health case in the last two decades, Duwe said: Michael Hayes, who shot nine people, killing four, in North Carolina in 1988.

Based on that, Holmes "faces some pretty long odds," he said.

Holmes was arrested almost immediately, while stripping off his body armor in the parking lot outside the Century 16 movie theater where he replaced Hollywood violence with real human carnage. His victims included a 6-year-old girl, two active-duty servicemen, a single mom and an aspiring broadcaster who had survived a mall shooting in Toronto. Several died shielding friends or loved ones.

Nearly three years passed as both sides filed hundreds of motions in legal debates over capital punishment and insanity pleas.

Prosecutors will argue that the once-promising doctoral candidate in neuroscience plotted and planned for months, amassing guns, ammunition, tear gas grenades and enough chemicals to turn his dingy apartment into a potentially lethal booby trap that could have caused even more carnage.

They'll ask jurors to find him guilty, and if so, sentence him to death rather than life without parole.

If jurors decide instead that Holmes was insane at the time of the shooting, he would be committed indefinitely to a state psychiatric hospital.

Dueling mental health evaluations could influence their deliberations. Judge Carlos A. Samour Jr. ordered a second exam after prosecutors said the first was biased. Defense attorneys have objected to the results of the second one.

These and many other details remain under seal.

Holmes faces 166 counts, including first-degree murder, attempted murder and an explosives offense.

It took nearly two hours for the judge -- who is presiding over his first death penalty trial -- to reach each charge, naming each victim, out loud during a pretrial hearing.

Holmes' trial could take at least four months or more and is sure to be emotionally wrenching. The 12 jurors and 12 alternates -- chosen from a pool of 9,000 because it was so difficult to find people who weren't personally affected -- won't know if they'll join the deliberations until after the trial.

Some survivors want Holmes executed, even if that means reliving horrific details.

"It still doesn't bring him back, but we want justice," said W. David Hoover, who wants to avenge the death of his 18-year-old nephew, A.J. Boik. "Real justice is going to happen when this animal leaves this Earth."

Fire Chief Larry Trujillo, whose daughter, Taylor, survived the shooting when a friend threw her to the floor, said while entering the courthouse that his faith enables him to forgive, but that this may be easier for him to say: His daughter survived.