This is the editor's letter in the current issue of The Week magazine.

Stephen Paddock left us a note. It provides no motive, but may still explain why he transported nearly two dozen weapons of war to his Las Vegas hotel room last week and turned an outdoor concert into a live video game, firing at 22,000 human targets, killing 59 and wounding nearly 500. The note, police say, consisted of a series of numbers that were the results of complex calculations: his elevation above the ground, the distance to the crowd, the angle of the bullets' drop to the flesh below. Paddock was "a numbers guy," a professional gambler who played high-stakes video poker for 14 hours straight and didn't much like anyone. In City Journal, Seth Barron offers the theory that Paddock's relentless pursuit of the dopamine hits that come with nonstop gambling left him with "no remaining capacity for pleasure or novelty." So for one last rush in an empty, blackhearted life, Paddock carefully planned and carried out a spectacular slaughter. His biggest jackpot ever.

We may never know for sure what drove Paddock to kill, but this much is certain: Mass killings are a malignant meme deeply lodged in our nation's psyche. Paddock had no apparent racial, religious, or political grievances, but no doubt felt the same transgressive thrill as the faux warriors who shot up Columbine, the Pulse nightclub, the Aurora movie theater, the Charleston black church, the Newtown elementary school, the San Bernardino conference center, and other domestic killing fields. What these mass killers had in common was profound alienation from a world that seemed indifferent to their pain and humiliation, and easy access to weapons that amplified their rage. Radical Islam, white supremacy, and other ideologies can serve to justify violent vengeance, but they are optional. Paddock didn't need reasons; he just assembled an arsenal and did the math. For damaged souls in whom empathy has died, inflicting misery can be its own reward.