CENTENNIAL, Colo. -- Jurors only needed 12 hours to reject the idea that James Holmes was legally insane when he slipped into a Colorado movie theatre's midnight premier of the Batman movie "The Dark Knight Rises," and opened fire killing 12 and injuring scores of others.

Now, the trial enters a new phase that is certain to take much longer, as the jury decides whether Holmes should die for his crimes.

Starting next week, jurors will hear testimony about Holmes' mental illness and his childhood. Prosecutors may counter with even more heartbreaking accounts from victims, ranging from those Holmes maimed to the father of his youngest victim, a 6-year-old girl who died in the 2012 attack.

There was a muted, heartbroken sense of relief Thursday afternoon following Holmes' conviction on 165 counts of murder, attempted murder and other charges. Victims wept and comforted one another in the courtroom during the hour-long recitation of each verdict, holding hands and nodding their heads with satisfaction when their loved one's names were read.

"We're all really happy he's guilty, but we're all really sad to be here," said Katie Medley, whose husband, Caleb, uses a wheelchair after being shot in the head during the attack.

The verdict came after 2 1/2 years of legal skirmishing between prosecutors and Holmes' public defenders and 11 months of grueling testimony. The upcoming sentencing phase could easily take another month.

"I'm glad we're at this point, but at the same time, we have a long way to go," said Marcus Weaver, who was injured in the attack and whose friend Rebecca Wingo was killed.

Experts say the sentencing phase could prove even more emotionally wrenching as survivors describe the impact of the shooting on their daily lives. It will be a harder decision for jurors, who will have fewer instructions to guide them, said defence attorney Karen Steinhauser, who is not involved in the Holmes case. That jurors swiftly rejected Holmes' insanity defence doesn't mean they'll come to a speedy conclusion about his punishment.

"They're going to have to decide, for someone who is mentally ill, if a death sentence is the right punishment," she said. "It ends up being a much more personal decision."

If just one juror disagrees with a death sentence, Holmes, 27, will be sent to prison for life.

For almost an hour Thursday, Judge Carlos A. Samour Jr. read charge after charge, reciting the name of the victim, the offence and the word "guilty." Dressed in a blue shirt and khakis, and flanked by his public defenders, Holmes stood impassively with his hands in his pockets the whole time.

The rest of the courtroom was bursting with emotion. Even before the verdict was read, jurors passed around a box of tissues and dabbed their eyes. The foreman attended Columbine High School during the 1999 shooting there that left 13 dead.

When Samour read the first finding -- that Holmes was guilty of first-degree murder for killing Jonathan Blunk, a 26-year-old father of two who shielded his girlfriend from the gunfire -- many victims' families burst into sobs, trying to stifle the noise by pressing tissues to their noses and mouths.

When Samour read the name of another murder victim, Jessica Ghawi, her mother, Sandy Phillips, silently mouthed "yes," and her husband wrapped his arm around her to pull her close.

"We're very happy this animal, this monster, will never see the light of day," Phillips said later outside court. "It feels good to have this weight off our backs."

Holmes' parents, Arlene and Robert, sat silently holding hands throughout the verdicts. After the final count was read, Arlene buried her face in Robert's shoulder.

The trial offered a rare glimpse into the mind of a mass shooter, as most are killed by police, kill themselves or plead guilty.

Prosecutors argued that Holmes knew exactly what he was doing when he methodically gunned down strangers as they fled. They painted him as a calculated killer who sought to assuage his failures in school and romance with a mass murder that he believed would increase his personal worth.

He snapped photos of himself with fiery orange hair and scrawled his plans in a spiral notebook he sent his psychiatrist just hours before the attack, all in a calculated effort to be remembered, prosecutors said.

Holmes' lawyers argued that he suffers from schizophrenia and was in the grip of a psychotic breakdown so severe that he was unable to tell right from wrong -- Colorado's standard for insanity. They said he was delusional even as he secretively acquired the three murder weapons and concealed his plans from friends and two worried psychiatrists.

The defence called a pair of psychiatrists, including a nationally known schizophrenia expert, who concluded Holmes was psychotic and legally insane.

But two state-appointed doctors found otherwise, testifying for prosecutors that no matter what Holmes' mental state was that night, he knew what he was doing was wrong.

Associated Press writers Sadie Gurman, Dan Elliott, Ivan Moreno, Kristen Wyatt and Colleen Slevin contributed to this report.