Downey Jr and Gyllenhaal sign to Zodiac
The film, to be directed by David Fincher the man behind Seven and Fight Club, will tell the true story of the serial killer who murdered at least 37 people in San Francisco in the 1960s and 1970s, yet was never caught.
Gyllenhaal, who has appeared in The Day After Tomorrow and Donnie Darko, will play Robert Graysmith, a reporter from the San Francisco Chronicle who investigated the murders at the time.
Downey Jr, the Oscar-nominated star of Chaplin, will play his co-reporter Paul Avery.
The script written by James Vanderbilt has been based on two books, Zodiac and Zodiac Unmasked: The Identity of America's Most Elusive Serial Killer Revealed, both written by Graysmith.
It is also hoped that Collateral star Mark Ruffalo will sign up to the project to play the murder investigator.
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