On NBC's Rock Center, an author who has spent many hours with Tom and Sue Klebold talked about what he's learned from them.
During the past six years, Andrew Solomon has had unprecedented access to the Klebolds.
"I had dinner with Sue last night," Solomon said. "She's soldiering on. It's a lot to bear, but she's a really courageous woman and she's tried to go on with her life."
In his new book, the Klebold's story is but ten pages out of nearly a thousand.
"When I went out to meet the Klebolds, I thought that if I got to know them, I would understand why this happened. And I would detect what was off in their household," Solomon said.
Instead, he says, he found a loving family.
"I think his parents had absolutely no idea. I think if they had known, they would have done something about it," Solomon said.
By the time the massacre was over, Dylan Klebold and Eric Harris had killed 12 students and a teacher, then turned their guns on themselves.
"Once I understood that it was actually Dylan who was doing this," Sue told Solomon. "I had to pray that he got killed before he hurt any more people. If he goes down, I wanna know it was his choice. So I hope he'll kill himself. And he did it. I was probably right. It probably was the best thing for him. But to have made that prayer and have that happen, it's a terrible thing to have to live with."
Solomon once asked Sue Klebold what she would ask Dylan if he were here now.
"She said, 'I would ask him to forgive me for being his mother and never knowing what was going on inside his head,'" Solomon said.