Despite that, his mother says he had been accepted to four colleges and was looking forward to attending the University of Arizona, and had attended his high school prom.
It was only in the days, weeks and months after her son's death that she learned the extent of his depression and his involvement in planning the shooting. Klebold and her husband had no idea that Dylan and Harris had been compiling a cache of weapons, and she had never seen the journal entries in which Dylan wrote frequently about suicide.
"Dylan's participation in the massacre was impossible for me to accept until I began to connect it to his own death," she wrote. "Once I saw his journals, it was clear to me that Dylan entered the school with the intention of dying there. And so in order to understand what he might have been thinking, I started to learn all I could about suicide."
She wrote that she never knew about his dark side.
"Yes, he had filled notebook pages with his private thoughts and feelings ... but we'd never seen those notebooks," she wrote. "And yes, he's written a school paper about a man in a black trench coat who brutally murders nine students. But we'd never seen that paper."
King said, "On the day when she went for the parent-teacher conference, they didn't have the paper there."
Brad and Misty Bernall, whose daughter Cassie was killed in the shooting, still believe Dylan's parents missed crucial signs.
"I can't help but think that a lot of this was preventable," Brad Bernall said.
Susan Klebold does partially blame herself.
"I often wished that I would die," she wrote. "While I perceived myself to be a victim of the tragedy, I didn't have the comfort of being perceived that way by most of the community. I was widely viewed as a perpetrator or at least as an accomplice since I was the person who had raised a 'monster.'"
She sent some of the victims and their families apology letters, but stopped sending them on her therapist's advice because some families found them unsettling.
"We've never received a personal apology from the Harrises or Klebolds," Misty Bernall said. "In those early days, it would've meant a lot."
But Brian Rohrbough, who lost his 15-year-old son Daniel, said he's relieved to finally hear from Susan Klebold.
"I'm happy to see it now," he said. "It appears to me that she is saying that she is doing this in hopes of preventing another suicide or another murder-suicide."
Klebold has struggled both with her grief and feelings of guilt about the shooting. Still, the family hasn't left the community and she now works to encourage suicide research, prevention and survivor support. Klebold hopes this will help other parents recognize the signs that she didn't.
"We should ask ourselves how good children are at hiding things," King said. "She said, 'we did not have those kind of clues.'"
Klebold wrote, "I concluded that he must not have loved me, because love would have prevented him from doing what he did. I'd failed to see that he needed help."
For the full essay by Susan Klebold, pick up the November issue of O magazine and visit oprah.com/essay