Why is Billy having second thoughts about his new job?

Billy is having second thoughts because Nick Majarian, a man who has hired him previously, is acting in a strange manner. Not only does Nick not seem to have all of the information about the shooting, but he also comes up with an escape plan for Billy, a part of the shooting Billy is generally left to take care of on his own. Billy has the sense that the people Nick claims will drive him to safety after Allen is dead are going to kill him.