In Doctor Sleep when Dan and Billy attack the True Knots with guns, why was Billy willing to shoot and kill people who he never met?
He generally seemed like a nice person and didn't even given them a chance to surrender. Also he hadn't given up hunting years ago, but Dan still asked if he kept guns in his car (I guess in some parts of the US it's common to have guns with you).
The best explanation I can come up with is, after finding the dead boy's body, Billy believed everything Dan had to say. Also it was stated he just had a good sense about people (but willing to kill is a bit extreme).
