Sam couldn't know for sure that Cady would get life in prison when he decided that sparing his life would actually make him suffer more. This is a man who wants to rape your wife and daughter and terrorize you until the end of your days--and you're willing to take a chance on the justice system doing the right thing?
He should have killed the sadistic & twisted Cady right then and there when he had the chance--he would have been justified in doing so!
True, but what really makes no sense is that Cady killed the cop assigned to watch over Sam's family. That's not just life -- that's a death sentence, even today, and certainly in 1962. Cady wouldn't have "rotted" in jail; he'd have been executed for that crime.
shareGreat point--thanks! I hadn't thought of that--of course, Cady would fry for killing the officer, and Sam would have known that. Maybe he just wasn't thinking completely clearly at that point? I still marvel at Sam's overall cool head at that particular moment--his family's been brutalized; he himself has almost died at Cady's hands just minutes before, yet he calmly thinks ahead. Gregory Peck sells it pretty well, though.
You're right, and Greg was always great.
I just posted two threads on the various crimes Cady committed, and for which he seemed to think he'd face no jail time: killing the cop, and his various sexual assualts. Cady's assumptions in committing these acts are the one big flaw in the film's plot, in my view.