The master is an evocative term for a suitably mysterious group. As the authors say, their study is necessarily based on failure: They can study only those who are caught. A master doesn’t find himself in court. While that ghostliness is a lure for fiction writers like me, it’s a frustration for researchers.

The problem with the best hit men is that the only thing we know about them is that they exist. We see their victims, and the victims’ cause of death, but that’s all. Unlike a researcher, tied to facts, a crime writer’s greatest thrill is perhaps mystery: Our hit man’s a blank canvas, to be decorated with the contents of our imagination. Maybe he starts as a novice, young and desperate. He develops and improves, and a degree of mastery slithers in and takes over.

The study points out that the single greatest tactic for avoiding detection is to never work in the area where you live. Move around, every job in a different place where you have no roots to trip over. The outsider. Perhaps a man of military background, working with military precision, but an outsider.

All of which is why our fictional hit men are a suitable distance from reality. Whatever type they fit, even the nonmasters, they have to stay masterfully free for at least 80,000 words.

The study describes the locations and manner of the hits as often “not unusual and extraordinary, but rather commonplace and ordinary.” It describes the reasons for many hits being ordered as “mundane.” Not descriptions creators of fiction want to carry with them.

So we read mountains of books about hit men, watch countless hours of them on screen. We play video games where we’re dropped into the role of the killer. Something draws us to these people in fiction. It’s the fact that, in reality, we would never do that job. There’s a line in the sand that a normal person won’t cross, no matter how desperate we are or how high the price.

That idea, of doing something so inhuman, makes the hit man intriguing. Getting close to the unknowable, creating a character who occupies the corners so dark no normal person can see into them. We don’t want to be hit men. We don’t find them glamorous; we’re repulsed by them. But we want to understand. As soon as we recognize something as being beyond our sensibilities, we have a need to learn why this isn’t the case for others. It isn’t a desire to see them succeed that leads us to crime fiction but rather the chance to stand close and watch how they fail. A need to understand that motivates researcher, writer and reader alike.

Malcolm Mackay is the author, most recently, of the novel “The Sudden Arrival of Violence.”