LOS ANGELES — The father of the young man who killed six people and injured 13 others near the University of California, Santa Barbara, last month says it’s his “duty” to help prevent future mass killings.

In a letter provided to ABC News on Friday, Peter Rodger wrote that he wants to help people recognize warning signs of mental illness within families.

He said his son, Elliot, hid his sickness from his parents, mental health professionals and law enforcement. In hindsight, the father said, he is beginning to understand there are traits, or “markers,” that family members can look out for in loved ones.

“My duty now is to do as much as I can to try and stop this from happening again,” the elder Rodger wrote. “It will be a long journey involving the personal choices of individuals and families, public discussions, mental health reforms, a change in the culture — you name it. My sincere hope is that I can help by telling my story.”

He said he has created a website — AskForHelp.org — with resources on mental illness and a place to share stories.