CENTENNIAL, Colo. - The much-anticipated disclosure came in a court hearing held four days after prosecutors publicly rejected an offer by James Holmes' attorneys that the former neuroscience graduate student would plead guilty to avoid execution.
Prosecutors had said the defense proposal wasn't a valid plea bargain offer, although they could still agree to a plea before the case goes to trial.
The decision to seek execution will delay the start of the trial until at least February, and the judge acknowledged even that might not be enough time for all sides to prepare. The trial had been planned to begin in August.
"It's my determination and my intention that in this case for James Eagan Holmes justice is death," Arapahoe County District Attorney George Brauchler said at the Monday hearing. He spoke quietly and deliberately without any hesitation.
There was no audible reaction from Holmes, who sat in court with his back to reporters.
Holmes' parents sat side by side in the gallery, clutching hands with fingers intertwined.
They were also quiet, as were the victims in the courtroom when Brauchler disclosed his decision, which he said he had shared with no one.
He said he had personally discussed the case with 60 people who lost relatives in the shooting. Overall, prosecutors have consulted with 800 victims and relatives.
Bryan Beard, whose best friend Alex Sullivan was killed in the attack, was in an overflow courtroom during the announcement.
"I had a huge adrenaline rush," he said. "I love the choice, I love it, I love it ... I hope I'm in the room when he dies."
Holmes' attorneys are expected to argue he is not guilty because he was legally insane at the time of the July 20 shooting. They balked at entering that plea last month, saying they couldn't make such a move until prosecutors made a formal decision on the death penalty.
Investigators say Holmes methodically stockpiled weapons and ammunition for his assault on a packed midnight screening of "The Dark Knight Rises" and booby-trapped his apartment to explode and distract any police who responded.
Last week, prosecutors said they had rejected an offer from Holmes' attorney to have him plead guilty and serve life in prison, saying the offer wasn't a serious attempt at plea bargaining. They accused the defense of trying to gin up public support for a plea deal.