Zodiac, about four men who became obsessed with finding the Zodiac Killer, who terrorized San Francisco for two decades, opens this weekend. The film is based on the books Zodiac and Zodiac Unleashed, by Robert Graysmith. Graysmith was in town recently to talk about the film, and sat down with Cinematical for a chat.

(WARNING: There are minor spoilers in this interview. If you don't know anything about the Zodiac case, and you don't want to before you see the film, then please stop reading now.)

Cinematical:Let's talk about what it's like to see your book made into a film.

Robert Graysmith: The first draft of Zodiac was 1,200 pages long, and my editor would say, well that's a wasted page, and there would be an "X". Unfortunately, I took it literally – if there was an "X" on the page, I wouldn't use it, even it was good. Now that the movie's coming out, people ask me if there's going to be a reissue of the book with the movie; the book's never been out of print, it never stopped selling.

Cinematical: How was it working with David Fincher?

RG: Fincher – he was one of those kids in San Francisco during Zodiac, when Zodiac was threatening to blow up school buses. So he has a great love for that area. And he wanted to lovingly recreate San Francisco. I think in a lot of ways that David Fincher was so transformed by the school bus threats. I don't know if you read this recent article with him where he talked about feeling betrayed by his father for putting him on a school bus, where he could be blown up, when his dad freelanced and could have driven him. So this has been a long time percolating.

I used to sit there and watch him (Fincher) and think he should have been an artist, a painter. I got to sit there and watch sometimes, and he'd do like 35, 36 takes – that's very common for him. He doesn't move the camera, which I love, so all the actors are walking through the scene, and he's watching, watching. There's just something about it, he's not even sure what it is himself. But I got to where I could spot it, I'd say, yup, it's 14. And then he's say, okay, 14's a keeper. But then he'd shoot another 19 after that. He's a perfectionist, he's looking at the light, at the dust in the air, everything.

Much more after the jump ...