Heavy metal guitarist shot and killed onstage

I'm surprised things like this don't happen more often:

COLUMBUS, Ohio - A gunman charged onstage at a packed nightclub and opened fire on the band and the crowd, killing top heavy metal guitarist "Dimebag" Darrell Abbott and three other people before a police officer shot him to death, authorities and witnesses said.

I'm sure the story will come out, but could it possibly have anything to do with the anniversary of John Lennon's murder? Was someone else trying to be the next Mark David Chapman?