The FBI agent who coined the term ""serial killer"" boasts about his exploits--and for good reason. Modesty isn't Ressler's strong suit, as even the subtitle attests, but his career is packed with so many amazing episodes--well related here with the help of Shachtman (Skyscraper Dreams, 1991, etc.)--that the chest-beating is forgivable. Ressler's major contribution to criminology has been his pioneering work in psychological profiling, which he developed by visiting prisons and talking to scores of convicted killers. His accounts here of interviews with Charles Manson, Richard Speck, Ted Bundy, John Wayne Gacy, and others are told with a fine flair for drama--e.g., of being locked in a cell with 6'9"", 300-pound mutilation-killer Ed Kemper, who, when it was clear that guards weren't answering Ressler's call to open the cell door, threatened to ""screw off"" the FBI man's head. Myriad tales of how Resaler tracked down killers complement the jailhouse yarns and offer much insight into serial killers' minds. Of primary importance is to determine whether a killer is ""organized"" or ""disorganized,"" stresses Ressler, who goes on to explain that all serial killings are classified as ""sexual homicides,"" because at their root is a ""sexual maladjustment"" that ""drives"" the ""fantasies"" that are played out in death. As deeply as Ressler gets into killers' heads, though, he refuses to reveal much of his own here, offering no explanation other than ""fascination"" and ""interest"" for why he's devoted his life to a calling so dire and soulwearying that, as he emphasizes and as the title quote from Nietzsche concludes, one who follows it risks becoming ""a monster himself."" Gibbering horrors brought to heel, secrets of the serial-killer unveiled: a true-crime bonanza, though a bit more self-introspection would have iced the cake.