Why did Norton play a big role in The Pigman?
Norton Kelly is a kid who is headed for real trouble. While John and Lorraine toe the line and get into problematic situations, they are basically good and well-meaning at heart. Norton, however, is hard core, and John ascribes to him sociopathic characteristics. John says about Norton,
"now his eyes even drift out of focus when you're talking to him. He's the kind of guy who could grow up to be a killer."
When John and Lorraine get to know the Pigman, they develop a genuine relationship with him. When Norton hears that they visit the old man, however, his only thought is to wonder if he has anything worth stealing. Norton is a bully and a thief, and he is causes substantial and intentional damage at Mr. Pignati's house during the fateful party thrown by John and Lorraine. Norton steals an expensive piece of equipment and destroys the old man's precious pig collection out of sheer meanness; he subsequently gets into a fistfight with John, just as the Pigman, frail and sick, returns unexpectedly from the hospital.