Prey(1979)

A rock singer who has returned to the U.S. approaches his former musician friends with the soulful sound of reggae that he encountered during his stay in the U.S. However, his friends lost their old energy and were busy chasing only the songs that would sell, and did not pay attention to reggae. Eventually, the lonely and violent rock singer turns to mass indiscriminate murder out of repugnance to the blurred times and humanity.