Which version of why Billy was shot is true?

Billy says its because Brandon stole guns from his car..or at least intimated that's why.
The Whites claim its because of a bad deal over a truck and gun. On top of that they claim that Billy said something about his dead father.


Why would Billy lie about why Brandon came for him? I can understand Brandon's mother and his cousins lying and saying Billy provoked him into doing it.

You never hear from Brandon why, just that he went up there and he was doped out of his mind and doesn't 'really know why I did it."

Either way he seems somewhat remorseful. Then in the next breath he blames his family for making him that way. Not that they helped any, they're all pretty crazy.