There is a chance Jason was in the car, but there is no doubt in my mind, or the evidence, that he did it.
He murdered her, after an argument at the front door, by slitting her throat from behind (little to no blood in the rear) and then killing him after a brief struggle by the bushes. He had dozens of stab wounds, so I believe OJ thought he was the latest beau (young, handsome, showing up at her door at night, she was scantily clad). I don't think there was a rage, but a red mist (that he was known for. She was a battered wife and he thought he was above the law because they always let it go, and she came back!) that doesn't necessarily equate to rage. I think he was angry when he killed her and had to cover up for her murder by murdering him.
Surely, the Bruno Magli shoes, the fact there was any blood in the car, the fact that he cannot account for his whereabouts at that time, the blood on his socks, the fact that the majority of his clothes were never found (most believe Kardashian got rid of them for him), the repeated lies (to the police, no less) about how he cut his hand, and the Bronco chase, etc, etc, etc...
Guilty as sin, and after a brief stint for armed robbery and kidnapoing, he will be out and about as if it all never happened! Remorseless psychopath who doesn't identify with his black heritage, yet uses it as a tool to self-aggrandize. Bad, bad man....but the world is full of them!