The film""s well-written screenplay (by Borden Chase and Charles Schnee) was based on Chase""s novel/Saturday Evening Postserialized story (in six installments from December 1946 hrough January 1947):The Chisholm Trail.While Graham was in FBI Headquarters in Washington DC, Crawford informed him that a "fan letter" had been found hidden in Lecter""s cell, presumably mailed to him from the Tooth Fairy." [The orderly fell bloodied to the ground and soon died of his fatal injuries - an accidental death when he fell on broken glass.]B-movie lead character Humphrey Bogart, now introduced as a ""good guy"", presented the definitive anti-hero Sam Spade in he mystery thriller classic - as a cynical, cool San Francisco sleuthing private-eye who lives by his own code of ethics.