The killer in Dirty Harry (1971) was loosely based on the so-called Zodiac Killer. Very loosely. The deviations start in the opening scene, as the killer–called “Scorpio” in the film–uses a high-precision rifle to kill someone in a hotel rooftop swimming pool and leaves a note demanding the city pay him $100,000. In the last scene, Clint Eastwood’s Harry Callahan captures, shoots, and kills Scorpio (right after reprising the most famous line of the film: “Ask yourself one question: ‘Do I feel lucky?’ Well, do you, punk?”). Nothing of that corresponds with the real-life Zodiac, who killed at close range, didn’t ask for money, and was never apprehended or even conclusively identified.

But the parallels were close enough for the screenwriter and director of the 2007 Zodiac (James Vanderbilt and David Fincher) to use Dirty Harry as an ironic counterpoint to the real-life police officers their film portrayed. The key cop in Fincher’s film is San Francisco Police Department Inspector Dave Toschi (Mark Rufalo), whose previous previous cinematic connection is mentioned in Zodiac. One character notices the way his gun is upside-down in a shoulder holster and says, “He wears his gun just like Bullitt”–the title character of Steve McQueen’s 1968 San Francisco-set cop movie. Another replies, “No, McQueen got that from him,” which is apparently true.

In Zodiac, years of going by the book and following up fruitless leads starts to wear Toschi down. His supervisor urges him to take some time off: “Go to Candlestick [home of the Giants baseball team], see a movie.” We cut to a marquee announcing a special screening for the S.F.P.D. Whoever selected the film for the screening probably meant well but made a kind of cataclysmic blunder, with the choice of Dirty Harry. We see Toschi, seated next to his wife, slumping deeper and deeper into his seat till he has to leave–one imagines that the fantasy of a cop taking the law into his own hands is simultaneously alluring and offensive, yielding a cognitive dissonance that’s hard to bear. He walks out to the lobby; he’s still there, smoking a cigarette, when the film ends. The mayor walks by and says, “Hey, that Harry Callahan did a hell of a job with your case.”

Toschi: “Yeah, no need for due process, right?”

Robert Graysmith (Jake Gyllenhaal), a San Francisco Chronicle cartoonist who has become obsessed with the Zodiac case, joins Toschi and tries to offer some encouragement: “You’re gonna catch him.” As he walks out, Toschi responds, “Pal? They’re already making movies about it.”