Character motivation etc.

I liked the movie, but what kept it from being truly great for me was the weak character motivation. All through the movie, I was waiting for the big reveal of the actual crime and why it had traumatized Dwight and his sister so much. I thought maybe they were kids and they watched their parents not only murdered, but tortured in front of them. I thought maybe Dwight was hanging out with the Cleland kids, and that involvement led to the murders, thus leaving him wracked with guilt.

I know everybody's different and people react to similar events in various ways, but let's face it a lot of people lose loved ones in violent ways and their lives don't go off the spool like Dwight's did. Dwight and his sister were walking around like PTSD sufferers. They couldn't stand the thought of guns, he destroyed one in the beginning, though he quickly got over it. And if family meant so much to him how come he abandoned his sister? How come they didn't cling to one another as the sole survivors? Then he goes out and revenge kills the wrong person, setting off a chain of events that put his sister directly in harm's way.