The highlight in history from The Associated Press for Friday reads:  On Dec. 14, 2012, a gunman with a semi-automatic rifle killed 20 first-graders and six educators at Sandy Hook Elementary School in Newtown, Connecticut, then committed suicide as police arrived; the 20-year-old had also fatally shot his mother at their home before carrying out the attack on the school.

It is hard to imagine that sort of hate or disregard for another human, especially 6- and 7-year-old children. No motive was ever determined in the massacre, but documents released include writings by the shooter: “I incessantly have nothing other than scorn for humanity,” the Hartford Courant reported. “I have been desperate to feel anything positive for someone for my entire life.”

On one handwritten list titled “Problems,” the shooter details a range of grievances including lights that are too bright and his hair touching his brother’s towel, The Associated Press reported.

“I am unable to distinguish between my problems because I have too many,” the shooter wrote.

It is clear he had deteriorating mental health problems, was isolated and was obsessed with violence. A report by a Connecticut child advocate said those things, combined with access to weapons, was a “proved recipe for mass murder.”

But that combination does not always result in tragedy. The nation, and especially the family members of those slain, will likely never fully understand what drove the shooter to murder on that day.

But we owe it to those children and teachers to keep searching for answers. We owe it to them — and to students and teachers everywhere — to find ways to keep schools safe.

Sandy Hook was not the first school shooting. It was not the last. But the slaughter of 6- and 7-year-olds sticks with us years later because it seems unimaginably horrific.  Let’s hope it continues to remain with us. It would be a tragedy if the nation forgets the slaughter of these innocent lives and does nothing to ensure it won’t continue to happen.