They just don’t make serial killers like they used to. Once upon a time, deranged maniacs like David Berkowitz or Richard Ramirez could paralyze an entire city with their murderous antics. But with the advent of cell phones, DNA testing and other innovations, such menacing characters are largely a thing of the past.

With his latest movie, Zodiac, director David Fincher (Se7en, Fight Club) revisits the still-unsolved case of one of the most notorious serial killers of all time. Culled entirely from real-life events, the film stars Mark Ruffalo (Just Like Heaven) as Inspector Dave Toschi, a San Francisco homicide detective who spent several excruciating years of his life trying to track down the elusive killer.

It's a new kind of role for Ruffalo, and the veteran actor made sure he showed up prepared. In addition to spending significant time with the real-life Dave Toschi, he scoured through countless case files as part of his research for Zodiac. "There’s a mind-boggling amount of material around this case," says Ruffalo. "I have the entire investigation sitting at home in a murder book, and I probably have more information than any one particular police department has because the one thing we were able to do was to get all of them to cooperate with the making of the movie but none of them cooperated with catching the guy."

Part thriller, part crime drama, Zodiac chronicles a time when most of America was unaware that such a monstrous person could exist. "The word ‘serial killer’ hadn’t been invented yet," explains Ruffalo. "Certainly there were serial killers, but they hadn’t popped up into the culture the way this guy did. He’s the first dude who sort of popped up into the minds of the culture and used the media and all of this to get himself off."

"Real life is infinitely more interesting than we can try to imagine," adds Ruffalo. "Fincher just painstakingly went and created that world, that time which we all have touched or known. We remember it. It has almost a sentimental value to most of us. He really did his work to recreate the time and the feeling."

Fincher's commitment to accuracy impressed Ruffalo. "He really was true to the investigation," he says. "There’s not one dramatic departure for the sake of dramatization in the movie. Which is pretty remarkable, I think, for something that spans such a long period of time."

Over his career, Fincher has earned a reputation as an exacting, intense and often mercurial director. "I was kind of scared to work with Fincher," Ruffalo admits. "I had heard that he was an intense guy and sometimes he yelled at people. So I didn’t know what to expect, but I was really surprised by how gentle and easygoing a guy he is."

Fincher is also known for riding his actors hard, often ordering countless takes. But Ruffalo wasn't fazed. "I come from the theater, man -- you do five hundred performances," he boasts. "Dave expects the best from people. He wants you to show up and be ready to work. He wants the best from people. He uses the best people and he expects the best from them."

"It can be nerve-wracking at times but I’m game for that journey," the actor adds. "I dug it. It gives you another chance to get it right."

Though the case remains officially unsolved, Zodiac hints strongly that Arthur Leigh Allen -- a prime suspect who died of a heart attack in 1992 -- was the culprit. Ruffalo, however, isn't so sure. "I keep flopping back and forth on it," he says. "I know they did this genetic test but we don’t know that it was his saliva on the back of the stamp. I have seen this guy. He was a bad, bad dude. He was a sociopath."

Zodiac opens nationwide on March 2nd, 2007.

Check out ReelzChannel.com's Zodiac page for clips from the movie and more.