A memorial service for those killed and injured in the Columbine school shooting in 1999. (Susan Biddle/The Washington Post)

Sue Klebold is author of “A Mother’s Reckoning: Living in the Aftermath of Tragedy.”

I am not an expert on guns. I have never owned one, and my husband and I never kept one in the house. So when it comes to gun safety and reducing the number of mass shootings that take place in our country, I would be the last person to suggest there are easy answers. But I do have a tragically personal vantage point on the issue.

Nearly 17 years ago, my son Dylan, and his friend Eric Harris, walked into Columbine High School carrying an array of firearms and explosives. They killed 12 students and a teacher and wounded more than 20 others. It was an incomprehensible tragedy that I have lived with every day of my life since. Why did Dylan do it? How could this have happened? These questions have consumed my every waking moment.

Gun rights advocates, and many legislators, say that the solution to stopping horrific shooting tragedies such as Columbine or Sandy Hook or Charleston or Santa Barbara or San Bernardino or Roseburg is not to restrict or regulate our access to firearms, in violation of the Second Amendment of the Constitution, but to focus more attention on mental health. Guns don’t kill people, people kill people, they claim. In the tragic instance of a mass shooting, guns are merely the instruments of a disturbed mind. And in fact, the overwhelming majority of gun owners act responsibly and safely. They would never fire on an innocent person, much less a child in a school. By focusing on guns, gun rights activists say, we miss the real challenge we need to address: identifying and getting help for those at risk because they are not brain-healthy.

And that is the approach I have taken in thinking about Columbine and my son. A number of factors brought Dylan to Columbine High School that morning to hurt his fellow classmates. There were the deep depression and suicidal thoughts that he had been living with and that I was unaware of. There was his distorted belief that he was unloved and unlovable. There was the bullying that made him feel like an outsider at Columbine to an extent I will never know. There was his friendship with Eric and the ways each reinforced the anger and pain of the other.

After spending the past decade interviewing experts, analyzing Dylan’s journals, talking with my family members, revisiting the days and years leading up to Columbine and working with others in suicide prevention, I realize there were signs, however unclear, that I might have recognized, knowing what I know now. But it was only after my son took part in what at the time was the worst school shooting in history that I — or anyone else close to Dylan — had any idea that there was anything wrong with him. Before Columbine, I would have told you with absolute certainty that I would know if there were anything amiss with my son, and even more so if anything were seriously wrong. But that raises an important question with regard to gun violence: If there are no flashing neon signs to alert us when someone needs help, how can we know who is and who is not mentally stable enough to be responsibly armed?

I’m convinced that by recognizing the signs that a child is struggling early on, we can get our children the help they need — before another Columbine takes place. So I am firmly in the camp of those who say we must focus more attention and resources on those who suffer from mental-health issues. I applaud the fact that since Columbine, a growing number of schools are making strides in identifying when kids are in crisis. But much more needs to be done.

Having said that, I still cannot help but believe that Dylan and Eric would not have been able to take the lives of so many if they had not had such easy access to guns. As I later learned, Dylan and Eric — both of whom were minors — secretly attended a gun show where they bought the shotguns they would use in the massacre and met a young man who sold them a TEC-9 semiautomatic pistol.

Is our right to gun ownership under the Second Amendment so absolute that we cannot, at the very least, restrict access to certain kinds of weapons to protect the most vulnerable among us — especially teenagers, whose judgment at the best of times is compromised by hormones, impulsivity and immature decision-making? Is our right to bear arms so vital to what it means to be an American that there can be no limit on those rights whatsoever, whether raising the legal age at which one can purchase a gun, as we did with the drinking age or conducting more extensive background checks or restricting access to assault weapons designed for the battlefield?

Again, the issues are challenging, and both gun rights advocates and gun-control advocates have valid points of view. I only know that every night as I go to bed, I can’t help but see the face of my son and the faces of the 13 people he and Eric killed and wonder what might have been.