CENTENNIAL, Colo. — Prosecutors this morning said they will seek the death penalty against the man accused in last year’s movie theater attack that killed 12, wounded 70 and spurred new gun control laws in Colorado.

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.

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.

The massacre was repeatedly cited by gun control advocates who pushed a hotly contested package through the Colorado state Legislature last month. The bills include a ban on the sort of high-capacity magazines that Holmes allegedly used to spray the theater with dozens of bullets in a matter of seconds.

As the tangled case against Holmes returns to court, survivors and families of the victims are uncertain about what happens next.

If the case goes to trial, “all of us victims would be dragged along potentially for years,” said Pierce O’Farrill, who was shot three times.

“It could be 10 or 15 years before he’s executed. I would be in my 40s and I’m planning to have a family, and the thought of having to look back and reliving everything at that point in my life, it would be difficult,” he said.