Recently bought the DVD of David Fincher's Zodiac, which is based on the true story of a serial killer who shot or stabbed his victims in and around San Francisco in the sixties and seventies. Starring Jake Gyllenhaal, Robert Downey Jr. and Mark Ruffalo, the film is classic Fincher, concentrating heavily on the hunt for the killer (similarly to Fincher's earlier film Se7en) and full of dark humour (similarly to Fincher's earlier film Fight Club). It also has strong overtones of neo noir or even sunshine noir, reminiscent of Chinatown. The way the investigative plot is handled is also strongly reminiscent of All the President's Men, which depicts two reporters investigating and eventually exposing the Watergate scandal of the Nixon administration.
Like many serial killers, including the famously elusive Jack the Ripper, the Zodiac wrote taunting letters to the police and the press, particularly the San Francisco Chronicle. He also sent codes and ciphers, including the one above. Robert Graysmith (played by Jake Gyllenhaal) worked at the San Francisco Chronicle and became obsessed with the case, eventually writing the book that the film is based on. Like most true crime books it's a bit convoluted, and obsessively detailed; the Zodiac case, which remains unsolved and highly contested to this day, took over a lot of lives. The main cop in charge of the case was Inspector Dave Toschi, played by Ruffalo (interestingly, Clint Eastwood's character in Dirty Harry was based on Toschi; the killer Clint Eastwood hunts in the film, Scorpio, is also loosely based on the Zodiac).
Although the Zodiac was never caught, the film concentrates on the man most people, including Graysmith, believe was the Zodiac; Arthur Leigh Allen, who died in 1992. Graysmith's book, first published in the seventies while Allen was still alive, uses fake names; presumably Graysmith's second book Zodiac Unmasked which I haven't read, published in 2007 (around the same time the movie was released) goes into more specifics. Anyway, check out the movie if you're into Fincher, horror, or detective stories.