Sue Klebold, Mother of Columbine Killer Dylan Klebold: 'It's Very Hard to Live With the Fact That Someone You Loved and Raised Has Brutally Killed People' Klebold says it's hard to live with the fact her son "brutally killed people."

 -- Sue Klebold, the mother of Columbine killer Dylan Klebold, told ABC News' Diane Sawyer that when the Columbine tragedy happened, she couldn’t stop thinking about the victims and their families.

“I just remember sitting there and reading about them, all these kids and the teacher,” Klebold said in an exclusive interview that will air in a special edition of “20/20” Friday at 10 p.m. ET on ABC.

“And I keep thinking-- constantly thought how I would feel if it were the other way around and one of their children had shot mine,” she continued. “I would feel exactly the way they did. I know I would. I know I would.”

On April 20, 1999, Dylan Klebold and Eric Harris opened fire at Columbine High School, killing 12 students and one teacher, and wounding 24 more people before taking their own lives. The tragedy not only shocked the community in Littleton, Colorado, but stunned the nation and forever changed how school administrations and law enforcement handle school shootings.

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

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

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

Before Columbine happened, Klebold said she was one of those parents who believed she would have known if something were wrong with her son -- but that all changed after the tragedy.

“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.”

This was Sue Klebold’s first television interview since the Columbine shooting. The interview coincides with the release of Klebold’s new memoir, “A Mother’s Reckoning: Living in the Aftermath of Tragedy,” out on Feb. 15. Her book profits will go towards research and charitable foundations focusing on mental health issues.

Watch Diane Sawyer's exclusive interview with Sue Klebold in a special edition of "20/20" Friday, Feb. 12 at 10 p.m. ET on ABC