The trial lasted 47 days, involved more than 250 witnesses and 1,500 photographs, and leaves a jury of 12 (winnowed down from a pool of 9,000 prospective jurors -- the largest in history) to contemplate 165 charges.

The critical question in all this is whether James Holmes could tell right from wrong when he entered the midnight showing of a movie in July 2012 and opened fire on the audience, killing 12 and wounding 70.

Should the jury declare Holmes not guilty by reason of insanity, he'll be sent to a state mental hospital. If he's found guilty, the same jury will hear testimony in a sentencing phase of the trial, and will decide whether to punish him with life imprisonment or the death penalty.

To decide the pivotal question of sanity, the jury will be asked to consider key evidence in the trial, including:

Dueling psychiatrists

Of the four psychiatrists who testified, two court-appointed experts assessed Holmes as mentally ill but legally sane , and two defense experts said he was insane .

As ABC News noted, all four experts agreed Holmes was mentally ill , but they disputed the extent of his illness.

Victims' testimony

Regardless of the clinical assessments, jurors are likely to have a hard time detaching their emotions from the grueling, heart-wrenching testimony of shooting victims. Among those is Ashley Moser , an expectant mother who was paralyzed in the shooting and miscarried her unborn child. Her 6-year-old daughter, Veronica, was killed.

Though Judge Carlos A. Samour Jr. instructed jurors not to let their sympathy for victims influence their verdict, that's easier said than done, said Valerie Hans, a Cornell Law School professor who is an expert on the insanity plea.

"This was a terrible tragedy in which great harm was caused for large numbers of people," Hans told The Associated Press. "It's virtually impossible to divorce that question of insanity from its context . I really feel for jurors who have to listen to wrenching testimony and steel themselves and look at the law and see which legal option really is the best match."

The notebook

Just prior to the shooting, Holmes sent a 29-page journal , full of his thoughts, shooting plans, and at times incoherent ramblings to the University of Colorado psychiatrist he'd been seeing. The notebook, in which he documented his "obsession to kill since I was a kid," never made it to his psychiatrist, and was instead found in the school's mailroom, unopened.

"The real me is fighting the biological me," Holmes writes in the journal. Later, he adds, "that's my mind. It is broken. I tried to fix it."

Holmes didn't testify during the trial, so the notebook provides rare, unfiltered insight into his thoughts and motives, CNN noted.

Holmes' therapist

The psychiatrist who treated Holmes before the attack spoke for the first time during the trial, relieved from the constraints of doctor-patient confidentiality by Holmes' insanity plea. During her time on the witness stand, Dr. Lynne Fenton recalled Holmes' frequent homicidal thoughts -- which she said were troubling enough to justify calling his mother -- but lacked the specificity necessary to warrant confining him on a mental health hold and contacting the police.

Fenton met with Holmes five times in 2012 from March to June, when he dropped out of his graduate program and lost his insurance. Though Fenton offered to continue seeing Holmes for free , Holmes declined.

At their last meeting, five weeks before the shooting, Fenton said she was concerned Holmes was shifting to a "schizophrenic state," reports ABC News. But she said there was no clear evidence he was an imminent threat to himself or others, so there was little she could do.

The jury is scheduled to begin deliberating the case Wednesday morning , following closing arguments on Tuesday.

AP reported insanity defenses are only successful about 25 percent of the time in felony trials nationally. The success rate declines further in high-profile homicide cases.