20/20 | 10pm on ABC

How long was Williams plotting his revenge against a television station that fired him in 2013? With all new details from the 23 page suicide note he sent to ABC News after the killings, “20/20” takes viewers from the single horrifying moment through the manhunt and into the mind of a killer.

Additionally, “20/20” examines anger management in the workplace. How do individuals and companies handle the difficult co-workers you work beside? Experts weigh in with information and tips viewers need to know.