David Shire composed the original score for Zodiac (2007). The score grew from sound designer Ren Klyce’s interest in Shire’s music for The Conversation; editor Walter Murch connected Klyce with Shire. Director David Fincher initially wanted no original score, then requested only 15–20 minutes of piano-based music, but Shire produced about 37 minutes incorporating textures from Charles Ives’s “The Unanswered Question.”
Shire described using a twelve-tone approach echoing the twelve signs of the zodiac — “There are 12 signs of the Zodiac and there is a way of using atonal and tonal music. So we used 12 tones, never repeating any of them but manipulating them” — and assigned instruments to characters: a trumpet for Dave Toschi, solo piano for Robert Graysmith, and dissonant strings for the Zodiac Killer. The performing orchestra drew on musicians from the San Francisco Opera and San Francisco Ballet.