Next spring will mark 20 years since two students — Dylan Klebold and Eric Harris — entered Colorado's Columbine High School and killed 12 students, a teacher and themselves.
They wounded 21 others, resulting for some in disfigurement and permanent disability. The psychological damage to others in the school and to rescuers can't be so easily measured.
Dylan's mother, Sue Klebold, has had a lot of time to think about, write about and study what she's called her son's "monstrous behavior," the loss of innocent lives and his suicide.
In that time, she's volunteered for suicide-prevention organizations, questioned experts, talked with fellow survivors of loss and examined the crucial intersection between mental health problems and violence.
After being so focused on the murders her son committed, she said, she had not considered the significance of his death by suicide, that killing himself had not been an impulsive act in the middle of this act of multiple murders, but part of a longstanding plan to go to the school to die.
Eventually, she got the courage to talk about what she had learned over those years and to publish a book, "A Mother's Reckoning: Living in the Aftermath of Tragedy," because the messages she hoped to convey, she said, were a matter of life and death.
Klebold is donating all author profits of her book to organizations that promote mental wellness, brain research and suicide prevention.
Thursday night, Klebold will speak at the CenterPointe Healthy Minds, Strong Communities Gala to advocate for mental health awareness and intervention.
In a 2016 TED Talk, Klebold said when she speaks, she doesn't know if someone in the room has experienced loss because of what Dylan did, and she apologizes to anyone there who was caused pain by her son.
In a phone interview Wednesday, Klebold said she hopes to communicate in Lincoln that what people see in others, and how they express themselves, may not always be what they are feeling on the inside.
"I want people to know that very often our loved ones are in great need, and we might not recognize that," she said.
She didn't recognize that in her son before he killed himself and murdered and harmed many others, she said.
Her own research on suicide and murder has shown her that a person like her son has to cross many thresholds to get to that place where they are able to kill. After the Columbine shootings, Klebold was shown some writings of Dylan's, two years before he died, that she hadn't known about before.
"He was writing about being very suicidal and wanting to die and being in agony, wanting to get a gun. And he wrote about cutting himself," she said.
With suicide, as well as some mass shootings that involve suicide, there's time to intervene, she said. And that's why it's so important that people learn better ways of being alert, responsive and knowing how to help before tragedy happens.
About half of the suicide loss survivors Klebold has met with know their loved one was struggling with mental health problems. Eric Harris had a psychiatrist and had been on medication. But the other half had no clue, she said, because certain behaviors, especially with adolescents, could seem like normal teenage behavior.
She missed a change of behavior, a red flag, in Dylan 14 months before the Columbine shootings when he got into trouble by stealing something with a friend and was arrested. He had never been in trouble before that, and she didn't see it at the time as a red flag.
Changes in sleeping, eating and isolating also can be somewhat typical adolescent behavior.
Parents need to listen, ask questions, dig deep, she said. People who are struggling need the best help available.
"We assume that our love is protective. We assume that if we love somebody enough, we can overcome anything or they can overcome everything. But love is not enough to help somebody who is struggling with thoughts that are poisonous and difficult. It's going to take some skills, as well."
According to the National Center for Health Statistics, from 2007 to 2015 the suicide rate for boys ages 15-19 increased 127 percent and 204 percent for girls 15-19.
People who are in that end stage of a crisis in which their lives are in danger don't have the ability to govern themselves or look at their situations objectively, she said. Their brains and chemistries are out of balance.
"All they want is for their pain to stop, their terror to stop, their rage, whatever it is," she said. "And very often they don't want anyone to know about it. ... They don't want to appear to be weak or to be a failure, or to perhaps have their jobs affected by admitting such a thing."
There's not much research about how someone crosses that line between killing just themselves and taking others with them. Each case is different and complex, she said.
In the case of Dylan and Eric, they had been bullied at school. Eric was filled with rage and his writings were graphically violent. He was highly motivated to kill and destroy, she said, and he was controlling.
Dylan was more depressed and wanted to die, she said.
"In Dylan's case, I think he was extremely angry," she said. "There's nothing that I can really do to understand what he did. I've been working on that for almost 20 years. ... All I know is it was the perfect storm of all these things being wrong. And it happened."