Twelve jurors failed to agree on a death sentence for Colorado theater shooter James Holmes on Friday, prompting shocked sobs from victims, police officers and his own mother. The former neuroscience graduate student will instead spend the rest of his life in prison for mass murder.

The nine women and three men said they could not reach a unanimous verdict on each murder count. That automatically eliminates the death penalty for Holmes, who blamed his killings of 12 people on mental illness.

The verdict came as a surprise. The same jury earlier rejected Holmes' insanity defense, finding him capable of understanding right from wrong when he carried out the 2012 assault that injured 70. Jurors also previously moved closer to the death penalty when they quickly determined the heinousness of Holmes' crimes outweighed his mental illness.

As the sentence was read, Holmes' mother, Arlene, who had asked the jury to spare her son's life, leaned her head against her husband's shoulder and began sobbing.

Tears broke out across the courtroom. In the back, Aurora police officers who responded to the bloody scene of Holmes' attacks began crying.

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.

Families of victims began to leave the courtroom as Judge Carlos Samour Jr. continued reading the verdict. Their wails were audible through the closed courtroom doors.

As in previous proceedings, Holmes, who is on anti-psychotic medication that dulls his responses, showed no reaction. His attorneys left court without commenting.

One juror told reporters outside court that there was a single juror who refused to give Holmes the death penalty and two others who were wavering. The key issue was Holmes' mental illness.

"All the jurors feel so much empathy for the victims. It's a tragedy," the juror said, refusing to give her name. "It's a devastating result no matter what. I am deeply, deeply sorry -- that isn't even the word."

The attorney for Holmes' family, Lisa J. Damiani, said in a statement that the family had nothing to say "other than to say that they are deeply sorry this has happened and they are so sorry that the victims and families have suffered such tremendous loss."

Prosecutors argued Holmes deserved to die because he methodically planned the attack at a midnight screening of a Batman movie, even blasting techno music through earphones so he wouldn't hear his victims scream.

District Attorney George Brauchler said Friday he was frustrated that Holmes didn't get the death penalty, but he praised jurors for doing a "hell of a job" throughout the grueling, four-month trial.

He also acknowledged rejecting an offer by Holmes' attorneys for a plea to life in prison without the possibility of parole. Brauchler said he did so because the defense refused to let Holmes be examined by a state psychiatrist and produce the notebook in which he explained the attack. Holmes was eventually subjected to two lengthy psychiatric evaluations and the notebook was entered as evidence.

"Because of that decision," Brauchler said, "the community now knows everything about this case."

The defense argued Holmes' schizophrenia led to a psychotic break, and powerful delusions drove him to carry out one of the nation's deadliest mass shootings. At least one juror agreed — the jury's verdict did not detail the split over Holmes' fate.

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

The verdict is the latest setback for the death penalty in Colorado, which has executed only one person since the U.S. Supreme Court reinstated the penalty in 1977. Gov. John Hickenlooper in 2013 said he would not carry out the scheduled execution of a man convicted of killing four at a Chuck E. Cheese in 1993.

There was never any question during the trial as to whether Holmes was the killer. He 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 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, Holmes 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 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.

He kept his mounting homicidal thoughts from a university psychiatrist, instead describing them in the notebook he mailed to her hours before the shooting.

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