Question: What caused Tom to start killing everyone?
Answer: It was many factors. First, he was blamed for letting the methane gas leak, which caused the explosion and deaths. Then, having one of the miners attack him and his friends. All that would cause anyone to go over the edge.
Answer: He had a psychological disorder which was triggered by the attack from Harry Warden. If I recall correctly, he developed a split personality.
ChristmasJonesfan