Let's write the unfinished sequel to Gilbert Grape (SPOILERS)
The local police investigate the fire and clearly determine it as arson. They find the body of Gilbert's mother badly burned and investigate the death as a homicide. Gilbert goes on the run and is one step ahead of the law. He travels around with Arnie before eventually ditching him at a bus station with deep guilt and remorse.
The law finally catches up with Gilbert and he is wrongfully charged with first degree murder. The movie finishes in prison.