The parents of James Holmes, who is charged with murdering 12 people in an Aurora, Colo., movie theater in 2012, say they feel partially responsible because they didn't realize that their son was mentally ill.

Prosecutors say Holmes tossed tear gas into the theater during a screening of The Dark Knight Rises and opened fire on moviegoers as they tried to flee.

"That's some of the guilt we have, that we didn't recognize he was ill and needed treatment," Arlene Holmes told San Diego's Del Mar Times. "Our kid was quiet, compliant, obeyed all the rules. He never bothered anyone, he never harmed anyone. ... Because so many people like to blame the parents if a child is mentally ill, we have to reaffirm to ourselves every day that we were good parents and good people, and this still happened anyway."

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At the same time, Arlene and her husband Bob are pleading with state officials and jurors to spare James the death penalty. "My basic feeling is it's immoral to have a state kill its own citizens, no matter what they did," Arlene says. "I've always thought it was wrong. Now I've had a lot of time to think about it, and how much it hurts people."

Last month, Arlene self-published a collection of her prayers called When the Focus Shifts, in order to advocate for people who are mentally ill.

In one of the prayers, Arlene addresses the lawyers who will be prosecuting her son. "I do not know why you want to pursue execution of a mentally ill man," she writes. "But I pray for you, so that you will find peace in your life. I pray you will change your mind. Please stop this quest for death so you may focus on those who are alive."

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Holmes' murder trial is set to begin April 27 in Colorado, but his parents say they're holding out hope for a plea deal in the meantime to spare themselves and the victims' families the added pain. "This would all come to a grinding halt if [James] could plead guilty, and the D.A. would accept the plea for life without parole," Arlene told the Del Mar Times.

A judge entered a not guilty plea in 2013 on behalf of Holmes, who is charged with 24 counts of first-degree murder (two charges for each victim).

Read Arlene and Bob Holmes' full interview here.

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