What about Sam at the end? (MAJOR SPOILER)
So, is the idea that he drowned when Barbra threw him off the dock? If so, wouldn't that get her put in prison for murder? And if not, if he survived, wouldn't he go right to the police and tell them what she did, thus getting her put in prison?
I suppose I'm stating the obvious here, but the inspiration for this film would seem to be the classic short story "The Ransom Of Red Chief".