In American Predator: The Hunt for the Most Meticulous Serial Killer of the 21st Century (Viking, July), investigative journalist Callahan exposes the stranger-than-fiction story of serial killer Israel Keyes.

How did you first learn about Israel Keyes?

In early December 2012, I came across an article about Keyes, and by the time I got to the second paragraph, I couldn’t believe what I was reading. Here was a serial killer with a completely unprecedented modus operandi, one who confounded the FBI’s top minds, who had no victim profile, who was active all over the United States for nearly two decades, and whose existence had been kept secret by the federal government for nearly nine months. There had to be a much more fascinating story here—or, as I suspected, multiple stories.

You call Keyes “a new kind of monster.” What do you mean by that?

I think of him as an analog killer in a digital age. Aside from the unprecedented m.o.—he killed all over the U.S., and probably internationally—he had no victim profile. Most serial killers operate closer to home. Most also have a type, but Keyes went after anyone, anywhere, any time: young, old, black, white, Hispanic, women and men, slim or overweight, well-off or vulnerable, alone or in couples, taking them from public places, or in their own homes, at night, in the predawn hours, in broad daylight.

To what extent did Keyes benefit from reading nonfiction books by law-enforcement professionals on serial killers and profilers?

He benefited enormously, and this is something even agents on this case didn’t know before: serial killers often learn from the good guys. Keyes told them that he read John Douglas’s Mindhunter as a teenager, and before then hadn’t realized he wasn’t alone. He also read Dark Dreams by the equally legendary FBI profiler Roy Hazelwood, and the minute Keyes said that, a couple of agents on his case ran out and bought the book. In fact, a few of them kept little libraries going, and whenever Keyes would reference a film or a book, each would add it to their personal syllabus.

Did TV depictions of serial killer cases help Keyes?

Keyes said he learned a lot about what not to do by watching CSI—a lot of criminals do, which explains why and how we’re building better monsters. But CSI also redounds to law enforcement’s benefit, because a lot of criminals think the FBI can do things that they actually can’t. And for a while the FBI was able to get information out of Keyes by referencing these CSI-ish powers that he assumed they had.