In Adaptation (2002), screenwriter Charlie Kaufman, the voice of weary experience, remarks that the serial killer is Hollywood’s hoariest cliché, the overexposed go-to-guy for the inspiration-impaired hack. Point taken—but the perp has certainly earned his star billing on the multiplex marquee. The serendipitous release in recent months of two serial-killer-centric DVDs—Don Siegel’s Dirty Harry (a two-disc edition and an "ultimate collector's edition" from Warner Home Video) and David Fincher’s Zodiac (Paramount Home Entertainment), a film from the 1970s and a film about the 1970s, both stalked by the same serial killer—traces the emergence of a predator whose criminal profile, once a blurry police sketch, has sharpened into a wanted poster more photogenic than the western outlaw, urban gangster, or corporate mobster.

The common source for both films—deep backstory for Dirty Harry (1971), narrative arc for Zodiac (2007)—is the Zodiac killer. In 1969, the Zodiac began a slow burn spree that claimed five (confirmed) murder victims in and around San Francisco, a relatively low body count that belies the city-wide terror incited by a territorial predator with a penchant for epistolary expression. Taking a page from Jack the Ripper, the self-christened Zodiac sent ominous ravings and coded messages to Bay Area newspapers, bragging of his homicides and threatening, in his most chilling taunt, to shoot children on school buses, or, as he phrased it, to "pick off kiddies as they come bouncing out.” Going on hiatus as suddenly as he opened fire, the Zodiac eluded capture and denied the reassurance of a case closed.

The investigation came to a more pleasing conclusion at the movies. In Dirty Harry, the opening salvo in what turned out to be a bellwether franchise for both Hollywood and Washington, a squinty, flinty Clint Eastwood incarnated a vigilante detective whose fidelity to Fourth Amendment niceties was retro even by 1972 standards. “Does Escobedo ring a bell? Miranda?” barks the exasperated DA after Harry tortures a confession out of his suspect-nemesis, a frothing psychopath named Scorpio (played with rabid relish by Andy Robinson), a Zodiac stand-in whose nom de plume also elegized an Age of Aquarius-Haight Ashbury scene gone bad. Though ripped from contemporary headlines, Scorpio could claim a long lineage in American cinema, from the psycho who pushed old ladies in wheelchairs down staircases (Richard Widmark in Kiss of Death, 1947) to the psycho who played old ladies in wheel chairs (Anthony Perkins in Psycho, 1960). In terms of temperament, MO, and clinical termscondition, Scorpio was a wack job, or, as Detective Callahan famously tagged him, a punk.

Yet even as Harry fired his .44 caliber Magnum into Scorpio’s chest, the smirking psychopath was being supplanted by a more lethal criminal type. Abetted by the mobility and anonymity of urban life, a feeding ground teeming with hapless prey (typically, young female hitchhikers), and a police force not yet equipped with computer databases, a cohort of less literary, publicity-shy serial killers thrived throughout the 1970s.

In the line-up of serial killers who prowled the decade, one, above all, came to personify the new public enemy in crime, culture, and cinema: Ted Bundy. The killer who made the term “sociopath” common parlance, Bundy was. unforgettably limned in Ann Rule’s true crime classic The Stranger Beside Me (in a hook no screenwriter would dare pitch, Rule shared duties with Bundy on a suicide hot line in Seattle in the early 1970s, when the aspiring law student and polite Republican initiated a rampage that, Rule believes, claimed upwards of 100 victims). Handsome, personable, and intelligent, he defied orthodox psychoanalytic explanation. In fact, that was the whole point: he was a sane man who killed because he chose to. In a career-risking performance in the TV movie The Deliberate Stranger (1986), the clean-cut Mark Harmon helped imprint the type with an expert diagnosis. “A sociopath,” Harmon-as-Bundy explains to a curious journalist, “has no conscience, no sense of guilt, empathy, no sense of consequences.” On the eve of Bundy’s execution on January 24, 1989, CBS News anchor Dan Rather called him the most hated man in America.

Though always more a creature of the imagination than of statistics (drug deals or marriages gone bad rack up a higher body count), the sociopath multiplied in proportion to a crime-weary nation’s impatience with the courtroom testimony of sociologists and psychologists who attributed a homicidal repetition compulsion to environmental deprivation or childhood trauma. The skepticism becomes a sneer in the Frontline documentary The Mind of a Murderer (1984), a case study of Kenneth Bianchi, the Hillside Strangler, yet another serial killer born of the 1970s, whose superior knowledge of psychology almost suckered a team of gullible shrinks into believing he had multiple personalities. “Maybe he’s just evil,” shrugs a wised-up psychiatrist, abandoning Sigmund Freud for John Calvin. Working the same vein, Jonathan Demme’s The Silence of the Lambs (1991) offered an instructive compare-contrast in the two serial killers lurking in their respective dungeons: one, the by-the-book psycho, Buffalo Bill, the other, the inscrutable sociopath, Hannibal Lecter, who is, with delicious irony, himself a psychiatrist.

Rendered almost cuddly by sequels and prequels, Hannibal Lecter has long since lost his sinister edge. In a true-crime matrix that stuffs the shelves at Borders, sustains basic cable programming, and supports countless really creepy websites, the sociopathic serial killer has proven domesticated enough to secure a place in prime time television with Dexter. Today a filmmaker who ventures into such well-trodden territory works not only in the shadow of Charlie Kaufman’s cynicism, but in a context where familiarity breeds contentment.

Zodiac refuses to play by the old generic ground rules. Adapted from the true-life thriller by Robert Graysmith, the film returns to the protean crime scene of San Francisco in the late ’60s and early ’70s, though with none of Dirty Harry’s cocksure arrogance. A work of historical excavation and moral rumination, it registers the shock of the new criminal type and the paltry resources of the detective work of the day. Zodiac himself is neither a crazed loon (Scorpio) nor a witty epicurean (Hannibal Lecter). Like his letters to the press, he is a cipher, a shadowy figure whose motives and personality are beside the point. Perhaps repenting for the deadly sins of Se7en (1995), his previous excursion into the serial-killer genre, Fincher refrains from stylizing the murders or doting on the murderer. The concern here is with the cops, the journalists, the victims, and the concentric waves of pain sent out by the killer.

Despite, or because of, the layers of police bureaucracy, it is an unequal contest: no wonder the game so gleefully baits the hunters. Highlighted by its absence is the forensic fetishism of the digital age. Only in a DNA-less, unwired world would a murderer who left behind so many clues leave the police clueless. Emphasizing the analog state of the art, the film’s production design lavishes loving detail on the low-low-tech communications hardware (there was no software) in the news-and-squad rooms of Nixon-era America, antique shops cluttered with clunky manual typewriters and boxes stuffed with paper records, before personal computers and palm pilots had revolutionized information processing (and before caffeine had supplanted nicotine and booze as the white collar drug of choice). Stripped of the sidearm accoutrements of their descendants, the forensically impaired police are forced to rely on 19th-century-minted tools like fingerprints and handwriting analysis. When the Zodiac sends his first coded letter to the newspapers, a clever montage shows the cryptographers at the FBI and CIA puzzling over the ciphers before visiting the breakfast nook of a frumpy schoolteacher and his wife—guess which experts crack the code.

To time-stamp the information gap, Zodiac ironically nods to two vintage Hollywood policemen: the hard-nosed, hard-driving detective played by Steve McQueen in Bullitt (1968), whose character was modeled after Dave Toschi, the San Francisco cop who would become obsessed with the Zodiac case, and (naturally) Dirty Harry. The physical prowess of Bullitt and Dirty Harry—maniacal driving, precision marksmanship, and brute force—is useless against Zodiac and his kindred quarries who must be swabbed, cross-referenced, and search-engined to be brought to ground. These days, forensic science and computer chops define the crime scene investigator: in whatever city CSI happens to reside, the geeks and lab rats do the heavy lifting, sniffing chemicals from the fingers of their white gloves and ziplocking DNA samples. By comparison, the cops in Zodiac seem as hobbled by their primitive methods of detection as the medieval monks in The Name of the Rose (1986).

Looking back at the cobwebbed ways of the not-too-distant past in Dirty Harry and Zodiac, one can’t help being struck by the dizzying pace of technological change in American life—the strange absence of computer screens, cell phones, and closed-circuit television cameras in an otherwise familiar environment. Still, no matter how dated the police procedures and office equipment, the one legacy from the Zodiac era that has not aged a whit, that seems totally in sync with our own time, is the profile of the serial killer and the cold verdict rendered on his kind, whether psycho or sociopath. “There are systematic inequities in the death penalty system,” says crime writer James Ellroy on the commentary track to the Zodiac DVD, "but motherfuckers like this have to die.”