Oops. Forgot a tag and a close quote. Let me try it again...
The shooter and the guard were having a disagreement.
The shooter wanted to take his gun into the office and use it to fire bullets at as many people as he could. The security guard felt strongly that this was not a good idea.
Words were exchanged and the situation escalated until it got out of control. Not much more to it than that.
Now please move along. There's nothing to see here.
Obviously, this gentle soul, who would get far more mental healthcare under ObamaCare, sought to have a calm exchange of ideas with the leaders of a right-wing hate group. He was rudely interrupted by a fascist sentry for said hate group, and sought to express his earnest desire for communication by firing his gun, which he possesses solely due to the evil efforts of yet another right-wing hate group. The fascist sentry jumped in front of the bullet which resulted in superficial wound (which will also be healed magically thanks to ObamaCare) although it's nothing compared to murderous mayhem caused by the far higher number of Romney-endorsing, NRA-loving gunmen that attack girlish congresswomen/human rights organizations, which normal people/liberals find deserving of sympathy, on a daily basis.
I took this directly from Soledad O'Brien's teleprompter.