The mother of Columbine shooter Dylan Klebold will give her first-ever TV interview Friday evening on ABC News’ 20/20.

The broadcast comes ahead of the publication of Sue Klebold’s book, A Mother’s Reckoning: Living in the Aftermath of Tragedy, available February 15.

In a prerecorded clip ABC released Friday morning, Klebold tells Diane Sawyer that when the Columbine massacre happened, she could not stop thinking about the victims and their families.

Image source: ABC News

Image source: ABC News

“I just remember sitting there and reading about them, all these kids and the teacher,” Klebold said in the exclusive interview.

On April 20, 1999, Dylan Klebold and Eric Harris carried out one of the deadliest campus shootings in U.S. history. The two teens killed 12 students and one teacher that day, and wounded 24 more people before taking their own lives.

The grim memories of that tragic day have remained with Klebold, whose family was criticized for their silence following the shooting.

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

The tragedy not only devastated Columbine High and the surrounding community of Littleton, Colorado, but it stunned the nation and had a permanent effect on 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,” Klebold told Sawyer.

“You used the word ‘harmed,’” 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,” Klebold admitted. “It is very hard to live with the fact that someone you loved and raised has brutally killed people in such a horrific way.”

Klebold was asked one particular question countless times in the years following the shooting: How could she have missed the warning signs?

Before Columbine, Klebold said she was one of those parents who thought she would have known if her son was acting out of the ordinary, but the massacre shattered that perception.

“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. “It’s very hard to live with that.”

Klebold told Sawyer that, before the attack, she felt like she was a good mother who was approachable and ready to listen to her son.

“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,” she said. “It was a completely different world that he was living in.”

Klebold’s first TV interview and book mark a new chapter in her life, moving beyond the shock of Columbine and focusing on preventing future tragedies.

Proceeds from her book will go towards research and to charitable foundations that tackle mental health issues. The 20/20 special will air Friday evening at 10 p.m. Eastern on ABC.

(H/T: ABC News)