More information on the attack and video of the incident
Shooter had a CCW and had just minor infractions. No motive yet. Maybe just snapped all of a sudden or gun store employees escalated something?
Nothing in the video or witness statements showed an altercation. Not even an argument. The guy had the pistol stuck down his waistband, not sure if he had a holster. The pistol had an extended mag -- you can easily see it in the video. When an employee saw the mag, he assumed it might be loaded and asked the guy if it was loaded. He said no. Then the employ said fine ... go out side to the clearing bin and clear it. And the guy went outside. No arguing or anything. But, that's when he fired a round in the air as he stood in the open doorway. Then he turned and fired into the woman he killed as she approached the door to leave.
This might have been a situation where he was just pissed at the world that day. Everyone he talked to told him what to do, what he can't do, and what he did wrong. Maybe the employee telling him he can't carry a loaded gun there was the last straw? I don't think anyone can tell us -- ever. Unless he left a note that's yet to be found, his actions have no rationale.
The second person he killed he shot in the back as the employee was crouched attempting to retrieve a firearm. That begs the question why the employees weren't wearing sidearms 100% of the time. When a bad guy starts shooting, you don't want to have to run to a lockbox or safe to get your gun if you can help it.
The Sheriff corrected his earlier account. Originally he told the press customers had engaged the shooter. In fact, only employees drew weapons.
I'm sure more details and corrections will come out.