Brennan Linsley, Pool, File, Associated Press
One prospective juror said she had a panic attack. Another claimed to have a bad back. A third is in the military and worried he would be deployed during the trial of Colorado theater shooter James Holmes.

CENTENNIAL, Colo. — One prospective juror said she had a panic attack. Another claimed to have a bad back. A third is in the military and worried he would be deployed during the trial of Colorado theater shooter James Holmes.

Even as an unprecedented 9,000 prospective jurors were summoned for questioning, both sides in the mass murder trial are worried about letting too many potential jurors go.

Prosecutors have asked the judge not to reveal why he releases jurors, for fear of handing out a road map for others trying to avoid serving.

And defense attorney Daniel King warned the judge who was listing off the reasons to let people go: "You have to consider the fact that people may not want to sit on this jury."

It won't be easy for those picked. Jury selection could last until June, and the trial could run into October. The court will pay jurors just $50 a day during that time, and employers only have to pay their workers for the first three days of jury service.

It's unusual for a mass shooter even to see a trial. Many killers take their own lives; others end up with plea agreements. Prosecutors in the Holmes case rejected a plea offer from defense lawyers, pushing the case toward a grueling trial that will replay the massacre.

The chosen 24, including 12 alternates, won't be allowed to talk to anyone — even each other — about the case, which means bearing the stressful experience alone. Mental health counseling will be available, but only after jurors reach a verdict.

"The length that you have to be on this case, and then to tell someone they can't talk about it, that is a huge burden," said Thaddeus Hoffmeister, a University of Dayton law professor. "Who wants to live in that bubble?"

The jury's job will be not only to decide whether Holmes was insane when he killed 12 people and wounded 70 others during the July 2012 attack, but they also might be asked to decide whether he should be executed.

Jurors will be shown graphic photos from the theater, where police say Holmes slipped in through a back door wearing a gas mask and body armor, threw gas canisters into the audience and opened fire during a midnight showing of a new Batman movie. They will hear harrowing testimony from people who scrambled for exits or dived for cover, shielding loved ones amid gunshots, screams and the blaring movie soundtrack.

Research has shown jurors in death penalty cases have suffered nightmares, flashbacks and symptoms similar to post-traumatic stress disorder, said James Acker, a researcher on death penalty juries at the State University of New York in Albany.

"They'll be barred from sharing what they're going through and thus not be able to share their feelings, either," Acker said.

Federal prosecutors in Boston are confronting a similar dilemma as they try to find people to serve as jurors for the murder trial of accused Boston marathon bomber Dzhokhar Tsarnaev, another death penalty case.

Some of those potential jurors have also cited personal hardships that would make it difficult to serve on the trial, which is expected to last three to four months. Several said they run their own businesses and can't afford to miss work, and others said they are the primary caregivers for their children, have prepaid vacations scheduled or have business trips planned.

The Holmes case is more challenging, as evidenced by the far greater number of jurors called. The 9,000 jurors — more than have ever been summoned for a court case in U.S. history, according to experts — represent nearly one out of every 50 residents of suburban Arapahoe County.

So many notices went out that witnesses to the attack received them, as did relatives of staffers in the district attorney's office. They were immediately dismissed. The number has already been whittled to 7,000 because many summonses were undeliverable.

Judge Carlos A. Samour Jr. had dismissed a total of 315 potential jurors by midday Monday. Most of the reasons haven't been made public, but a few people had doctors' notes, couldn't speak English, weren't residents of Arapahoe County or had pressing family responsibilities.

The potential juror excuses are treated with heavy scrutiny. Samour wouldn't dismiss a woman who said she was so sick she needed an ambulance; he just allowed her to come back another day.

The judge on Thursday dismissed the woman who complained of a panic attack after making her describe her condition under oath. Another woman also cited panic attacks as a reason she couldn't serve, but this time, Samour asked her to come back another day.

Excuses vary, and they show the broad cross-section of those called: One potential juror is the sole caretaker of his severely disabled wife. Another worried his orthodontics business would suffer. Another needed to find day care.

The financial strain will be difficult. Some businesses pay for more than the three days of service required by Colorado law, but many don't. That limits jury service to those who won't suffer serious financial hardship — retirees, government employees, those who work for large corporations — which can alter the panel, said Joseph Rice, managing partner of the Jury Research Institute, a California-based trial consulting firm.

"All of a sudden, you've taken a jury of your peers, which is supposed to be a random cross-section of the community, and now it has become dramatically skewed," he said.

Associated Press writer Denise Lavoie contributed to this report from Boston.