Nine of the 12 jurors in the Colorado theater shooting trial wanted to execute James Holmes, but one was steadfastly against the death penalty and two others wavering, a juror told reporters after the verdict was announced.

Because the 12 jurors failed to unanimously agree that Holmes should be executed, he will be sentenced to life in prison without parole for the 2012 attack on a midnight screening of a Batman movie in Aurora that also left 70 injured.

"Mental illness played into the decision more than anything else," said the woman, who would not give her name. "All the jurors feel so much empathy for the victims. It's a tragedy."

A juror told The New York Times that a fellow juror was solidly opposed to a death sentence. The juror said nine were in favor of the punishment, two were apparently on the fence about the decision.

"There was nothing further to discuss at that point," the juror said. "It only takes one."

The verdict came as a surprise. The same jury rejected Holmes' insanity defense, finding him capable of understanding right from wrong when he carried out the attack. It also quickly determined the heinousness of Holmes' crimes outweighed his mental illness in a prior step that brought them closer to the death penalty.

There were gasps and tears in the courtroom as the verdict was read. One man from the victim side got up and stormed out after the first one.

Bob and Arlene Holmes stood up with their son, arms around each other, and as the judge read the verdicts, she put her head down and started crying.

Holmes himself stood staring straight ahead as the verdicts were read, showing little emotion, but when he returned to his seat he leaned over to defense attorney Tamara Brady, grabbed her hand with a smile, and said "thank you."

Loud sobbing could be heard from the family section, where some sat with their heads in their hands.

The courtroom was also full of first responders, including Aurora police department officers -- some of whom cried along with the families as the verdicts were read.

Sandy Phillips, whose daughter Jessica Ghawi was killed by Holmes, shook her head no and then held it in her hands.

Ashley Moser, whose 6-year-old daughter died in the attack and who was herself paralyzed by Holmes' bullets, also shook her head and then slowly leaned it against the wheelchair of another paralyzed victim, Caleb Medley.

The sentencing hearing was scheduled for August 24, 25 and 26.

The defense had argued that Holmes' schizophrenia led to a psychotic break, and that powerful delusions drove him to carry out one of the nation's deadliest mass shootings. At least one juror agreed — a verdict of death must be unanimous.

Jurors deliberated for about six and a half hours over two days before deciding on Holmes' sentence.

They reached their decision after the judge granted their request earlier Friday to re-watch a graphic crime scene video taken immediately after the massacre. The 45 minutes of footage, played during the trial, shows 10 bodies lying amid spent shell casings, popcorn and blood.

There was never any question during the grueling, four-month trial as to whether Holmes was the killer. Holmes meekly surrendered outside the theater, where police found him clad head-to-toe in combat gear.

The trial hinged instead on the question of whether a mentally ill person should be held legally and morally culpable for an act of unspeakable violence.

It took jurors only about 12 hours of deliberations to decide the first part — they rejected his insanity defense and found him guilty of 165 felony counts.

The defense then conceded his guilt, but insisted during the sentencing phase that his crimes were caused by the psychotic breakdown of a mentally ill young man, reducing his moral culpability and making a life sentence appropriate.

The jury's final decision came after days of tearful testimony from relatives of the slain.

The case could have ended the same way more than two years ago, when Holmes offered to plead guilty if he could avoid the death penalty. Prosecutors rejected the offer. But the victims and the public might not have ever learned in detail what was behind the shootings had the plea deal been accepted.

The trial provided a rare look inside the mind of a mass shooter. Most are killed by police, kill themselves or plead guilty. By pleading insanity, he dropped his privacy rights and agreed to be examined by court-ordered psychiatrists. Holmes told one that he had been secretly obsessed with thoughts of killing since he was 10.

His parents testified that he seemed a normal, affectionate child who withdrew socially in adolescence and became fascinated with science but did not seem abnormal. Holmes studied neuroscience hoping to understand what was happening to his mind. But it was when he moved from San Diego to Colorado to attend graduate school that his meltdown accelerated.

Holmes flunked out of his prestigious doctoral program at the University of Colorado and broke up with a fellow graduate student, the only girlfriend he'd ever had. He began to buy guns and thousands of rounds of ammunition and scouted out The Century 16 theater complex to learn which auditorium would offer the highest number of victims.

Holmes also constructed an elaborate booby-trap in his apartment a few miles away. It failed to explode, but it was designed to blow up and divert police and firefighters at the precise moment of his calculated attack.

He kept his mounting homicidal thoughts from a university psychiatrist he was seeing. Instead, he described his plans in a notebook that he kept secret until hours before the attack, when he mailed it to the psychiatrist. In it, Holmes diagnosed himself with a litany of mental problems and methodically laid out his plans, even calculating police response times.

Four mental health experts testified that the shooting wouldn't have happened if Holmes weren't severely mentally ill. He was having increasingly palpable delusions that killing others would increase his own self-worth, forensic psychiatrist Jeffrey Metzner said.

Shortly after midnight on July 20, 2012, he slipped into the premiere of "The Dark Knight Rises," stood before the capacity crowd of more than 400 people, threw gas canisters, and then opened fire with a shotgun, assault rifle and semi-automatic pistol.

Fox News' Jennifer Girdon and the Associated Press contributed to this report.