The mother of Columbine shooter Dylan Klebold has said "never a day goes by" where she does not think of the people her son massacred.
She told told ABC News' Diane Sawyer: "I think we like to believe that our love and our understanding is protective, and that 'if anything were wrong with my kids, I would know.' But I didn't know, and it's very hard to live with that."
Mrs Klebold said she believed she was a "good mom", and that she thought Dylan "could talk to me about anything".
"Part of the shock of this was learning that what I believed and how I lived and how I parented was an invention in my own mind - that it was a completely different world that he was living in," she told ABC's 20/20 programme.
In the interview Mrs Klebold described how she had struggled in the years after the shooting.
The post, written directly to Mrs Klebold, included a copy of what Ms Hochhalter called a "genuine and personal" letter she received from the Klebold family months after the shooting.
In it, Sue and Tom Klebold wrote: "Though we have never met, our lives are forever linked through this tragedy that has brought unspeakable heartbreak to our families and our community.
"With deepest humility we apologize for the role our son, Dylan, had in causing the suffering you and your family have endured."
Mrs Klebold's interview comes ahead of the release of her new memoir, A Mother's Reckoning: Living In The Aftermath Of Tragedy.
Proceeds from the book, set for release on Monday, will be donated to research efforts and charitable foundations focusing on mental health issues.