I gleaned this from the article on backstage.com:
Gyllenhaal will play Robert Graysmith, the journalist and author of the two books, "Zodiac" and "Zodiac Unmasked," upon which the film is based. Downey will play fellow reporter Paul Avery, and Ruffalo would play the San Francisco homicide inspector in charge of the case.
And there's no word on shooting dates or locations, so keep 'em peeled, Beav!
Nothing precious, plain to see, don't make a fuss over me. Not loud, not soft, but somewhere inbetween. Say sorry, just let it be the word you mean.