The only time that John Kramer actually tried to kill someone was Detective Tapp

When Tapp and his asian cop partner got to that warehouse and tried to arrest Jigsaw but they were distracted by Jeff in the chair trap, that right there was the only time that John Kramer actually tried to kill someone, Tapp who was a cop.

Rewatching Saw 1, there were signs that John was getting sick from cancer while he was dealing with Jeff. also still surprised that John even made it out alive during that entire moment with Tapp and the cop partner