The mother of the man who opened fire in a movie theater in Aurora, Colo., in a 2012 incident that left 12 people dead is finally speaking out.

Arlene Holmes, mother of shooter James Holmes, spoke to ABC News affiliate KGTV in San Diego, saying that her lack of understanding of mental illness prevented her from spotting how serious her son’s mental illness was.

Holmes said that her mistake was to just keep going and to try to fix everything herself rather than seek out the help of a professional. She called her son’s actions “horrible,” and said that at around 12 or 13 years old he started to see a dark change in her son’s outlook.

They saw a family therapist for his sad outlook on life, but Holmes only got worse, becoming more quite, isolated, and irritable. He showed signs of psychosis in his early 20s.

Holmes said she decided to speak publicly now in order to “honor” those who died at her son’s hands. She said if she didn’t speak out, she wouldn’t be able to use his failure to provide advice for other people who might be going through the same thing.

James Holmes, 28, is currently in prison on a 3,318-year sentence for the killings, and was given 12 life sentences on top of that for each of his victims. They had been wathcing a midnight showing of The Dark Knight when Holmes entered the theater and started shooting.

Holmes has been transferred to an undisclosed maximum-security prison after he was assault at the Colorado State Penitentiary last year.