Screenwriter Richard Tuggle spent six months researching and writing a screenplay based on the 1963 non-fiction account by J. Campbell Bruce. He went to the Writers Guild and received a list of literary agents who would accept unsolicited manuscripts. He submitted a copy to each, and also to anybody else in the business that he could cajole into reading it. Everyone rejected it, saying it had poor dialogue and characters, lacked a love interest, and that the public was not interested in prison stories. Tuggle decided to bypass producers and executives and deal directly with filmmakers. He called the agent for director Don Siegel and lied, saying he had met Siegel at a party and the director had expressed interest in reading his script. The agent forwarded the script to Siegel, who read it, liked it, and passed it on to Clint Eastwood.
Eastwood was drawn to the role as ringleader Frank Morris and agreed to star, providing Siegel direct under the Malpaso banner. However, Siegel insisted that it be a Don Siegel film and out-maneuvered Clint by purchasing the rights to the film for $100,000. This created a rift between the two friends. Although Siegel eventually agreed for it to be a Malpaso-Siegel production, Siegel went to Paramount Pictures, a rival studio and never directed an Eastwood picture again.