Many things in this movie didn't make sense because it just wasn't very good... How this has a 6.9 is mind boggling...
If Michael Bay ever directed a boring film that went on way too long, this would be it...
They killed them for their car, and also because Dafoes character accidentally called Grot and said he was an inbred.
shareI'm gonna copy paste my reply from another thread to here. Tell me what you all think.
DeGroat is a *beep* psycho. He says that Willem Dafoe's character still owes him money, the Willem says "That's it, that was the deal, we talked about this"
I guess it's just up to your personal interpretation. They both seem equally sincere in their belief, before DeGroat pretends to let it drop. My personal theory is DeGroat is too stupid, inbred, and intoxicated to remember what they talked about. He was drinking when they met after the drive down when it was light out, and still drinking when the fight was over that night. And you know how he gets when he's drunk (opening scene).
Regardless, DeGroat has a genuine belief that Dafoe's character still owes him money (we ain't square mother *beep* As far as Casey, you can't leave witnesses.