<Li> Robert Downey, Jr. as Paul Avery, a journalist at the San Francisco Chronicle who covered the Zodiac killer case . </Li> <Li> Anthony Edwards as SFPD Inspector William Armstrong . When casting the role, Fincher said he thought of Edwards because "I knew I needed the most decent person I could find, because he would be the balance of the movie . In a weird way, this movie wouldn't exist without Bill Armstrong . Everything we know about the Zodiac case, we know because of his notes . So in casting the part, I wanted to get someone who is totally reliable ." </Li> <Li> Brian Cox as Melvin Belli, a prominent defense attorney who received a letter from the Zodiac killer . </Li> <Li> Elias Koteas as Sgt . Jack Mulanax, a police detective from Vallejo . </Li>

Who plays the zodiac killer in the movie