Biggest Question in Dark Knight Shooting Trial: Why?

The trial of James Holmes begins today, nearly three years after he massacred moviegoers in Aurora, Colo. The case has been in what the Denver Post calls "a kind of cocoon " since soon after the 27-year-old killed 12 people and injured 70 others during a midnight showing of The Dark Knight Rises, but the public will learn much more about it in the days, weeks, and months to come as evidence sealed so jurors wouldn't hear about it elsewhere finally sees the light of day. "We will understand if there was a mental disorder. We'll have a much better understanding of what he is thinking and what he is believing," University of Denver psychologist Dr. Neil Gowensmith tells the Post, though he warns that the big question of why Holmes carried out such a horrific act may never be fully answered.

Holmes has been charged with 164 counts of murder and attempted murder—two for each person killed or injured. His attorneys do not dispute that he carried out the shooting, but, over what is expected to be a harrowing trial lasting four months or more, they're expected to argue that the graduate student was insane, meaning he should be committed to a psychiatric hospital indefinitely instead of executed, the AP reports. "Obviously, this defendant is not normal. Obviously, he has mental health issues. The question is: Does it rise to the level of insanity under Colorado law? Could he tell right from wrong?" a former chief deputy district attorney in Denver tells NBC News. (Holmes' parents say he is not a monster and argue that the state should accept a guilty plea in return for life without parole.)