All the characters were basically normal people who made bad decisions when under various forms of stress (death of child, marital problems, over-work, etc).
At first I thought the only ones exempt were Claudia and Paula d'Amato. But even the latter contributed in a small way to the confusion. By threatening to cut her husband's balls off if he messed with their marriage, she probably decided him not to admit he had picked up a woman late at night. Although he knew he did it in all innocence, he might not be sure that she would think so.
Subconsciously, John Knox probably wanted to "punish" his wife. She had emotionally shut him out and had just falsely accused him of having an affair (a homosexual one at that). But then expects him to jump to bail her out when she has a problem. The worse he thought would happen is that she would be an hour late home. He might also have known she was prone to exaggeration and hysteria, as the scene where she screams at a perfectly innocent woman shows.
Not the right way to feel, for sure, but very believable. How often in marriages does one partner "punish" the other for real or imagined slights? And how often does this result in fatality?

You do see how guilt-ridden and gutted John is by the end.
To his credit he fesses up to Leon about ignoring her call for help, even when he probably didn't need to.

On the other hand, he heard her saying that a car approached and he thought she was coming home. Like he said to the detective.

Rush`s character was apparently undergoing a serious mental short circuiting or an emotional paralysis thers. Such things, and worse, do happen.
"facts are stupid things" - Ronald Reagan

yeah or get her home and don't talk. it was mentioned on another thread that basically his careless behavior effectively aided her death. This callousness is what caused the Lapaglia character to finally breakdown and have his breakthrough.
remember he was a tough guy and he couldnt understand why the guy cried when he broke his nose, but he held him anyway. Although he wss tough he was a cop and it was his instinct to protect those that needed protecting. Like pete said sometimes you just feel like crying.
You can live on fishes but you can't live on wishes

I agree. Nevermind the tension between them, the woman's car broke down and she's stuck in the middle of nowhere! Get her home first and talk later.