The jurors who convicted James Holmes of murder in the Colorado theater shooting were still deliberating Thursday in the first phase of his sentencing, taking more time than expected to decide whether prosecutors proved at least one legal requirement for a death sentence.

Prosecutors said several of these "aggravating factors" were proven beyond a reasonable doubt when Holmes opened fire at the midnight Batman movie premiere: the outsized number of victims, the fact that he killed a child and the particularly heinous nature of the attack.

They said Holmes wanted to murder as many as he could in the audience of more than 400 people but failed to kill more than 12 because his assault rifle jammed.

The defense offered no counter-argument, effectively conceding that prosecutors had met the first of several requirements for the death penalty. But jurors went home before deciding whether prosecutors had met their burden Wednesday, and resumed deliberations Thursday.

It's the first of a three-step process to determine whether Holmes should be executed or sentenced to life in prison without parole for the 2012 attack, which also maimed 58 people and injured 12 more.

Prosecutor Rich Orman on Wednesday showed jurors photos of each person killed and read their names — bringing some of their relatives in the courtroom to tears. Holmes deliberately and cruelly killed all of them, including 6-year-old Veronica Moser-Sullivan who "had four gunshot wounds to her little body," Orman said.

Orman reminded jurors that Holmes threw tear gas and sprayed so much gunfire that even moviegoers hiding behind seats couldn't avoid being hurt.

"The victims were unaware of any danger, watching a movie, in a theater, a place of joy and of safety," he said. "The victims died surrounded by screaming, by pain and by anguish."

Assuming jurors agree there were aggravating factors to justify the death penalty, the defense will lead the next phase, trying to show that his mental illness and other factors make it wrong to execute him.

Jurors would then deliberate for a second time, deciding whether the extent of his mental problems outweighs the lifelong suffering Holmes caused. If so, the trial would end there, with a life sentence instead of the death penalty.

If not, the sentencing will move into a third and final phase, in which victims and their relatives would describe the impacts of Holmes' crimes.

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Associated Press writer Dan Elliott in Denver contributed to this story.