The police have identified the gunman in the LA Fitness shooting as George Sodini. He is among those who died. A note was found in his gym bag but authorities has not released its content yet to the public. There are rumors that one of those who died in the shooting is Sodini's ex-girlfriend. Sodini is a member of the gym.
Sodini has maintained a blog that can give clues to why he did what he did. I tried to access his blog but it is down now. But there are texts from his blog that are blockquoted in other blogs so you might as well search for it.