I had never read about that before. That's actually really sad.
Believing that people on the television are conveying subliminal messages to you is a textbook Schizophrenia symptom. I have worked with so many people who have expressed similar beliefs.
Unfortunately, despite sounding really farfetched and delusional to most people, such things appear real to the person experiencing them. Tragically the distress these experiences cause people is also very, very real and can drive them to desperate actions.
Poor guy.