Brandon Doherty is a severely depressed and violent teenager with a history of suicidal ideology, homicidal thoughts about his classmates, and depression he channels to internet livestreams. His therapist was Dr. Isaac Waxman, who didn't place him on any psychiatric prescriptions and kept him on a vitamin-rich diet and meditation exercises. Brandon transferred to another therapist, but he still called Isaac for consultation, including with regulating his new medicine.
Brandon was suspected when Dr. Waxman was shot dead in his office, as Brandon bought the gun used to kill him. What happened was Brandon wanted to commit a school shooting, but he only gave the gun to Waxman, who put it in his desk. When Brandon found out Waxman was dead, he nearly killed himself on another one of his streams by cutting his throat, but the detectives stopped him before he could go through with it.
Brandon was institutionalized and gave his full statement, clearing him of suspicion. (L&O: "Betrayal")