What is a twenty year old doing

[undeterred]

13. The age when the "first psychotic break" occurs can be around 20

and people can be pretty normal before that. Then they experience psychosis and are very dangerous.

Back when ER was on the air in the 90s they did an episode based on a true story in which a resident was stabbed to death in the emergency room by a patient who was seemingly worried about health issues but then became afraid the doctor was going to take his kidneys so he attacked him.

The doctor should have recognized the paranoia as a symptom.

Edit: Yes, Lanza shot himself when the police came to the scene.