In Saw II, Jigsaw shares a story with Detective Matthews about how he attempted suicide after his cancer diagnosis by driving his car off a cliff. We then see Jigsaw pulling a metal rod out of the left side of his stomach. However, no puncture wound/scarring is visible on Jigsaw's stomach when his autopsy is being performed.
When Officer Rigg is walking through the school, before he finds Morgan and Rex in the rod trap, he walks by a dark room blocked off with police-barrier-tape. Originally, there was a scene that revealed this was the room where Troy from "Saw III" died, but it was cut, presumably for pacing reasons.