In Saw III Amanda sets up multiple traps for Jeff, a father of two who lost his son to a drunk driver. In his trial Jeff meets some of the people responsible for his son's death as well as the people who let the driver off very easily. Jeff gets to decide if he can revenge on the people who have done him wrong or if he wants to forgive them.
Couple of notes (because you guys pick up on my mistakes very fast):
- Eric Matthews wasn't killed by Amanda, he appears again in Saw 4. There it's revealed that Amanda only knocked him unconscious and put him in a new trap. (But that doesn't change Amanda's intentions)
- The pipes in the meat locker weren't hot (that wouldn't even make sense), they're cooling pipes. When Jeff puts his cheek against it, his skin sticks to it.