Matthew McConaughey was originally cast as Freddie Lee Cobb. After reading the script, he preferred the role of Jake Brigance. He went to director Joel Schumacher, who granted him a private screen test.
Soon after the murders, Jake is tormented by guilt. He admits to Carla that he didn't tell anyone about Carl Lee's plans, because he didn't believe Carl Lee would go through with them. In the book, he does tell the Sheriff, but the Sheriff is the one who downplays the potential danger.
In this movie, Ellen Roark is so disgusted by the death penalty, that she almost quits trying to be on Carl Lee Hailey's defense team, when she finds out that Jake Brigance is very much in favor of it. However, in this movie, she is trying to get Carl Lee Hailey off a murder charge, when he killed the two men who raped his daughter. Essentially, she was trying to get someone off, who had executed a death penalty to two men for their crime, before they had been convicted or even tried.