DENVER — (CNN) Jurors in the death penalty portion of the James Holmes trial began deliberations Thursday in the mitigation phase.

For death penalty proceedings to continue, jurors must agree unanimously on at least one of Holmes’ 24 murder convictions that mitigating factors don’t outweigh aggravating factors.

If not, the trial is over, and Holmes will spend the rest of his life in prison without the possibility of parole.

Holmes opened fire upon a crowded movie theater just after midnight on July 20, 2012, as the audience watched the new Batman film “The Dark Knight Rises” in Aurora, Colorado.

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