Dylan Klebold and Eric Harris opened fire at Columbine High School almost 17 years ago, on April 20, 1999. They killed 12 students and one teacher, and wounded 24 more before they killed themselves.

Columbine killer Dylan Klebold's mother gave her first interview since the shooting in 1999. https://t.co/dq9MS6qDvy

— Complex (@ComplexMag) February 13, 2016

In a 20/20 interview with Diane Sawyer on Friday night, Dylan Klebold’s mother, Sue Klebold, recounts for the first time on TV, her feelings about whether or not she could have prevented what happened on that fateful day.

“There is never a day that goes by where I don’t think of the people that Dylan harmed,” Sue Klebold said.

“You used the word ‘harmed,’” Diane Sawyer noted.

“I think it’s easier for me to say harmed than killed, and it’s still hard for me after all this time,” Dylan Klebold’s mother said. “It is very hard to live with the fact that someone you loved and raised has brutally killed people in such a horrific way.”

17 years after Columbine, Sue Klebold speaks exclusively for the first time to Diane Sawyer: https://t.co/i0URFZe0J8 pic.twitter.com/8WGbXYSjwL

— ABC 7 Chicago (@ABC7Chicago) February 12, 2016

Prior to the Columbine shooting, Sue Klebold admits she was the kind of mom who believed she would have known if something were seriously wrong with her son. April 20, 1999 shattered that belief completely.

“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,” she said. “And…it’s very hard to live with that.”

“I felt that I was a good mom. That he would, he could talk to me about anything,” Klebold continued. “Part of the shock of this was that learning that what I believed and how I lived and how I parented was–an invention in my own mind. That it, it was a completely different world that he was living in.”

Sue Klebold has written a book called A Mother’s Reckoning: Living in the Aftermath of Tragedy. It goes on sale Monday.

Klebold received a huge gift on the day before her interview with Diane Sawyer. She received forgiveness from one of Dylan Klebold and Eric Harris’s victims.

Anne Marie Hochhalter was shot during the Columbine shooting, but lived. She is paralyzed–forever confined to a wheelchair.

Via social media, Hochhalter told Dylan Klebold’s mom that she doesn’t hold her responsible for her son’s actions. That may very well allow Sue Klebold to take the biggest step toward healing she has ever considered.