In TV land, this phrase is a convenient byproduct of a collective brainstorming session. But that’s not quite how the phrase came about in real life. In his 2003 book Serial Killers: The Method and Madness of Monsters , Peter Vronsky writes that the term “serial killer” was the brainchild of FBI agent Robert Ressler . Along with John E. Douglas , the author of the book Mindhunter, upon which the Netflix series is based, Ressler was the first to really study serial killers in earnest.