Who can understand the mysteries of the forces of darkness?"" So reads the diary of David Berkowitz, captured by New York City police in August 1977, after a year-long series of terrifying attacks that left six young people dead and seven wounded. Who indeed? Until he killed repeatedly, Klausner notes, Berkowitz ""slipped through the nets society sets to separate psychopaths from the rest of us."" In this painstaking, ""authorized"" (half the royalties go to the victims' families) account of the crimes and capture of the ""44 caliber killer,"" Klausner wisely avoids retrospective pop-psychology and sticks with the known. Always a loner, somewhat strange, Berkowitz handled reality somehow (he did a hitch in the army, attended a community college, served as an auxiliary cop) until ""demons,"" howling incessantly, sent him out to kill in the summer of 1976. There was no motive, no real pattern: ""It didn't matter who I'd kill, whoever I'd come across. . . . I thought of it as a job."" With a madman roaming the streets, a 200-detective ""Omega"" task force turned the city inside out, chasing down over 3,000 suspects (including one poor cop who was off-duty during each attack, and looked like some police sketches of the killer). Klausner's day-by-day account emphasizes the New York newspapers' role in heightening public fear (Jimmy Breslin, in particular, draws fire); he also stresses the mounting pressure on the police which turned an investigation into an obsession--some of the Omega group had to be ordered to go home occasionally. There were bizarre coincidences: plainclothesmen stopped Berkowitz, simply for looking suspicious, a few blocks from the scene of the fifth attack, only to be called away by the first radio report of the shooting; two Yonkers cops had been eyeing Berkowitz for two months before his capture, but he seemed simply a local nut until a parking ticket linked him to the neighborhood of the final attack. Son of Sam is can't miss material, and Klausner largely confines himself to laying out the facts (though he goes off the deep end once, stating in the prologue that the case against Berkowitz was so weak he ""probably would have been acquitted"" if he had gone to trial--a view supported nowhere else in the book). He avoids one obvious major question--why didn't Berkowitz plead not guilty by insanity?--and provides only the sketchiest account of the strange saga of Berkowitz's several lawyers. Workmanlike and readable? Yes. Definitive? No.