One thing changes the whole idea behind the character of 'Karl'...
Karl is portrayed to be this simple, slow, but good-hearted human being who has had a sad and rough life. He committed this horrible crime when he was a kid, but the murders that happened were a result of Karl walking in on a disturbing situation (his mother having sex with another man). So I took it as Karl reacted to what he was seeing and he he immediately took action and murdered his mother and this man.
Now fast forward to the end of the movie **Spoiler** where he has made a distinct decision to kill Doyle. That means that he took the time to think about it, whether he wayed the pros and cons, played different situations out in his head or not; he eventually came to the conclusion that he MUST kill this man in order to save the people he loved. To me, this just changes the character of Karl a little bit. If he had walked in on Doyle beating Frank or his mom, then I would have understood his motivation a lot more, it would have just made more sense to me. I know earlier in the day Karl saw Doyle put his hands on Frank, but Karl took action there and told Doyle not to do it again. There was no other event that sparked Karl's rage and violence.
I just always thought Karl reacted to a horrible situation when he was young, but he later learned that it was a "bad" decision and that he shouldnt have killed them. Maybe Im wrong, but it's just what I felt while watching it for the first time front to back...
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