For nearly 40 years, the world's greatest criminal investigators have pored over intricate, coded clues left by America's most notorious serial murderer -- the man nicknamed "The Zodiac Killer," who was responsible for between five and 39 deaths in the San Francisco area starting in the late '60s. Puzzled by his cryptograms, the San Francisco Police Department, FBI and CIA have been unable to discover his true identity.

Can you?

"Not only does the Zodiac Killer write letters, he's writing codes -- he says, 'My identity is in this code, and if you crack the code, you'll know who I am,' " screenwriter and producer James Vanderbilt said of the villain at the center of his new film, "Zodiac," which stars Jake Gyllenhaal, Robert Downey Jr. and Mark Ruffalo. "These codes have never been solved. Somebody could sit down today and figure out the Zodiac clues and do something that no one else has ever done. Look at the letters and look at the code and give it a shot."

It would be a Herculean effort, not least of all because the letters sent by the Zodiac Killer have baffled investigators for so long. A preternaturally intelligent stalker, the Zodiac Killer never even came close to being captured, in part because he didn't just defy convention -- he invented it.

"All modern serial-killer stuff comes from what Zodiac did -- he was the first person since Jack the Ripper to write letters and take credit for his crimes," Vanderbilt said. "Detective Dave Toschi [played by Ruffalo in the film] said [the SFPD] hadn't even ever heard of a serial killer. They called him 'that nut.' The terminology didn't even exist."

Vanderbilt credits today's familiarity with the terminology not just to the remarkable notoriety of the Zodiac Killer, but also to the films and books that have used him as an inspiration, including what he called "the two great serial-killer movies, 'The Silence of the Lambs' and 'Seven.' " The latter was directed by "Zodiac" helmer David Fincher.

"Fincher actually said, 'Listen, I'm not interested in making a serial-killer movie. I want to make the last serial-killer movie,' " Vanderbilt recalled. "He hates this genre. [He] wanted to close it out."

According to Vanderbilt, the choice of serial killer about whom to make the definitive serial-killer movie may have had much to do with Fincher's childhood in the San Francisco suburbs.

"David said that one of his earliest memories was being on a school bus with a police officer on the bus and a police car following," Vanderbilt said. "He went home and asked his dad what was going on, and his dad told him about [the Zodiac Killer], who had [threatened] to kill schoolkids. And that was a defining moment in his life as a kid, knowing that there was evil out in the world."

But while evil can be observed, it can't always be explained. Vanderbilt says "Zodiac," due March 2, avoids even trying.

"We don't do something like 'JFK,' where the movie exists in order to convince you of a premise," he said. "We never show the Zodiac doing something unless there is a survivor to explain what happened. We're trying to be incredibly accurate and truthful."

To that end, Vanderbilt tracked down the Zodiac's two known surviving victims, Michael Mageau and Bryan Hartnell, for help in making the film accurate. The pair couldn't have ended up in more disparate circumstances.

"Mageau was a trick to track down -- he's actually homeless right now," Vanderbilt said. "We only got 20 minutes with him at a correctional facility because he was picked up for vagrancy.

"Bryan was wonderful, and we spent a lot of time with him," he continued. "He's a jolly, great guy and has a wonderful family, but it's kind of tough to sit and have dinner with the guy -- at some point the conversation comes around to, 'So how were you stabbed?' "

Vanderbilt says the involvement of editorial cartoonist Robert Graysmith was also integral to the film. Played by Gyllenhaal, Graysmith wrote the "definitive work on Zodiac," a book that became the basis for the feature film, Vanderbilt asserted. Graysmith, a central figure in the early investigation, provided a way into the story that avoided most serial-killer-movie stereotypes.

"I felt like we've all seen the tortured-cop-chases-the-killer movie," he said. "What was sort of fascinating to me about Graysmith was that he was a [cartoonist]. We're talking about a guy who, on the one hand, was so amazingly unqualified to be going after a serial killer, yet on the other, he's someone who deals with images and symbols every day in terms of what he does for a living."

Graysmith claims to have cracked the 1979 Zodiac code. Regardless, police are no closer to catching the killer than they were 30 years ago.

"It's possible Zodiac never killed again, but that would be very odd because serial killers don't usually stop killing," Vanderbilt said, adding that it's very likely the killer is still out there.

And so far, he's gotten away with murder.

Check out everything we've got on "Zodiac."

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