The script took Schaefer four years to write, but when it was finished, the film came together quickly. With the help of producers Alexandra Milchan and Robert Salerno, Schaefer cast Jared Leto as Mark David Chapman. For his role, Leto gained by drinking microwaved pints of ice cream mixed with soy sauce and olive oil every night. Gaining the weight, he said, was tougher than dieting himself into skeletal shape for his role as drug addict Harry Goldfarb in "Requiem for a Dream" (2000). The abruptness of Leto's weight gain gave him gout. He had to use a wheelchair due to the stress of the sudden increase in weight put on his body.