They are angry at someone. Angry at the world. Angry at work. Angry at the way they were treated by their mothers, wives, whatever. The precipitating event just pushes them out the door.
Some people turn to alcohol or drugs to cope with the anger.
Others internalize it. And some end up committing suicide. So now they're going to act out these crimes. And there will be no remorse toward the victims. That's something they can't identify with because they consider themselves the victims.