Gary and Campbell were part of the Gang of Bullies that beat up Jeremy in the opening.
- The other bullies in that gang (apart from the leader Joe) were not named, and Jeremy has little reason to be going after Gary and Campbell in contrast to his other victims (the four girls who were his main targets, while Millie the housekeeper and Detective Vaughn were so he could move around the house easier, and Ruthie caught him in the middle of trying to dispose of Millie's body).
Jeremy murdered his parents.
- One of the articles Kate is reading mentions that Jeremy's parents died in a fire and that the circumstances were somewhat suspicious. It isn't too much of a stretch that Jeremy killed them for not doing anything to help him or not believing him.