The Daegu subway fire was a mass murder-suicide on February 18, 2003 which killed at least 198 people and injured at least 147. An arsonist set fire to a train stopped at the Jungangno Station of the Daegu Metropolitan Subway in Daegu, South Korea.
Lots of people murdered no guns used.
As for people changing with a gun in their hands. I agree, most people become a lot more careful.