On July 31, 1969, a letter arrived at the offices of the San Francisco Chronicle with the handwritten admonition: "Please rush to editor!" The contents of that letter would terrorize the residents of the San Francisco Bay area,and would forever change the lives of four men: flamboyant and ambitious Detective Dave Toschi, his partner, the quieter William Armstrong, star crime reporter Paul Avery, and, perhaps most unlikely of all, quiet, unassuming political cartoonist Robert Graysmith. Inside the envelope was the first letter from the serial killer who came to be known and feared as the Zodiac killer. In addition to the handwritten letter ("This is the Zodiac speaking ... "), the envelope contained one-third of a cipher. The other two parts had been sent to two other papers. In that letter, Zodiac took credit for two recent murderous attacks on young couples, which had left two women and one man dead.
The cipher befuddled every major law enforcement agency, but it was solved, oddly enough, by a history teacher and his wife (three other ciphers sent by Zodiac have never been deciphered). And it was the quiet cartoonist, Graysmith, who put together one of the first important clues to the killers MO: the cipher referenced a 1932 film called The Most Dangerous Game, about a man on a remote island who hunted people as prey. Zodiac, a killer so wily and clever (and perhaps just a little bit lucky) that he managed to elude police for over two decades, taunted the cops with their failure to find and stop him. His threats to blow up school buses or to shoot out the tires of buses and then "pick off the little kiddies as they come bouncing off the bus" paralyzed the city, forcing police car and plane escorts for the city's schoolchildren.