I MAKE my living writing about a serial killer. It’s a pretty good living, and quite frankly, that surprises me. When I wrote my first book, “Darkly Dreaming Dexter,” the story of a sympathetic killer, I thought I was writing something creepy, repellent, perhaps a little wicked. To balance that, I also made him vulnerable and funny, I gave him a fondness for children, and I wrote in the first person — all elements intended to bridge the gap between a homicidal psychopath and readers, who I assumed would, nevertheless, be appalled.

They weren’t; they liked him. Before publication, a nice-looking yenta from marketing took me aside and confessed, “I maybe shouldn’t say? But I have such a crush on Dexter.” So did other readers. The book took off like a dark little rocket. One of the early reviews even said it “breathes new life into the genre,” which meant there was a serial killer genre.

I found that amazing: I had done the darkest, least lovable thing I could think of, and a whole genre was there ahead of me.

People, I realized, like to read about serial killers. And as I found myself on the telephone with Hollywood, arranging for Dexter’s translation into a series for Showtime, I began to think that was pretty funny. “Lovable serial killer.” Ha ha ha.

And then bodies turn up in real life and it isn’t funny anymore.

This time, it’s along a beach on Long Island. Our shock blooms as phrases pop out from the news coverage: “at least eight bodies” and “three or even four killers.” We read more — we can’t help it. We’re sickened and disgusted, but we need to know. And the more we know about the scene, the more we really are horrified. The ghastly image of this beach as a dumping ground for bodies is bad enough. But then four of the bodies, wrapped in burlap, are thought to be the work of one person: a serial killer.

There’s a special sense of dread that comes with that phrase, “serial killer.” It represents an inhuman psychology that is beyond us, and because of that, we can’t look away.

We can all conceive of killing someone in self-defense, or in combat. But to kill repeatedly, because we want to, because we like to — that’s so far outside ordinary human understanding that we can’t possibly have an empathetic response. The word “evil” seems a bit quaint and biblical — but what else can we call it?

I was brought up to believe that death and money are private, and I was taught to have only contempt for people who slowed down to gawk at an accident. I can’t help feeling that this is similar — but I watch, too. Have I become what my mother called a rubbernecker and what my father, more bluntly, called an idiot?

Maybe so, but I have lots of company. Not just Americans, either; the Dexter series has been translated into 38 languages, and sensational news of serial killers regularly floods in from Russia, China, all over the world. People everywhere are willing voyeurs to mayhem. And when we learn of serial murders like the recent case at Gilgo Beach, our “dark watcher,” that small part of us that just can’t turn away, perks up and pays attention.

This isn’t necessarily a bad thing. We don’t become evil because we dwell on it. In fact, one reason we gawk is to reassure ourselves that we could never do such a thing. When we stare at carnage we feel fear and revulsion, and that tells us with certainty that creating this kind of horror is beyond us.

And it is. Serial killers are psychopaths, and current research in brain mapping indicates that psychopaths are born, not made. There is an actual, physical, difference in their brains; you can’t become a serial killer by reading about one, any more than you can get magical powers from reading “Harry Potter.” You can watch “The Texas Chainsaw Massacre” 20 times and it will not inspire you to butcher the neighbors. We can no more move from watcher to killer than we can breathe water.

But a homicidal psychopath — a serial killer — delights in killing. He often taunts the rest of us in some way as part of his fun. The evil creature that has been dumping bodies on Gilgo Beach has used his victim’s cellphone to call her sister.

It’s inhuman cruelty, but the research I read to write my “Dexter” books predicts that, when they catch him, he will probably look just like us. He will be known as a charming and thoughtful co-worker, a nice man who helps his ailing neighbor carry her groceries, and no one will have suspected what he really is.

This is the theater of paranoia, and it grips us, too, because we need a way to see the clues that must be there. Who among your friends and colleagues might be staring at your back and sharpening a knife?

You can’t know; but by watching, you know it could never be you. I think that’s good. We can’t deny that evil exists — but it’s not who we are. And the existence of evil implies its opposite: there is good, too.

As ordinary human beings, we live somewhere in the middle, jerked back and forth by circumstance, never quite reaching either extreme. And if you never understand someone who lives at the evil pole, no matter how much you rubberneck, that’s good.

It means you’re only human.