Although David Fincher's excellent new film covers countless aspects of the infamous Zodiac killings, one interesting area of the case goes largely unacknowledged. For while he had a frightening interest in butchering his fellow Californians, the man in the black hunting garb was also a huge movie fan.

Sure, Fincher's film makes something of the killer's interest in The Most Dangerous Game - Ernest B Schoedsack's superb adaptation of Richard Connell's classic short story - but there's no mention of the murderer's passion for contemporary cinema. The Zodiac was in fact such a big cinemagoer that, when he wasn't writing to the San Francisco papers about his latest exploits, he sent them notes about the hot motion pictures of the day.

Not all of these missives were positive - despite having no problem with blowing cab drivers away at point blank range, the Zodiac was critical of Terence Malick's Badlands and the San Francisco Chronicle's decision "to run ads for the movie featuring the blurb 'In 1959 most people were killing time. Kit & Holly were killing people.'"

Continued the killer, "In light of recent events, this kind of murder-glorification can only be deplorable at best... Why don't you show some concern for public sensibilities & cut the ad?"

If the butcher didn't like Malick's dark road movie, he seemed much more positive about William Friedkin's The Exorcist, a film he described in a letter received on 30 January 1974 as "the best saterical [sic] comidy [sic] that I have ever seen."

And there you were thinking Mark Kermode was the world's most (in)famous Exorcist fan. If the Zodiac's affection for Friedkin's film seems odd, it's no less strange what happened next. Obsessed by the Zodiac case, Exorcist author William Peter Blatty built 'Legion', his follow-up novel, around a killer not unlike the one then terrifying Northern California. This book would later become the film The Exorcist III (1991), a picture which stars Brad Dourif as a serial murderer known as the Gemini Killer. Fast-forward 15 years and David Fincher's Zodiac is sent out to American cinemas with a false name to deter piracy. The pseudonym in question? Gemini.