Seems like a justified shooting
It seems there's testimony from 3 witnesses that say Scott drew his gun, so if that's true it makes more likely to be a justified shooting by the police. If, as witnesses claim, he pointed his weapon at the officers, they were completely within their rights to shoot him. It's quite possible, with the style holster pictured in the blog, that he managed to withdraw the entire holster with the gun, but I think it would be hard for the officers to quickly see that the gun were still holstered if he were pointing it at them. Even if he pointed the holstered gun at the officers, they would seem to have reasonably concluded he was pointing a gun at them to shoot them with it. While it's unfortunate, and it seems like Scott was not trying to threaten or shoot the police officers, from what evidence has been submitted thus far it seems like the officers were justified in responding to the call as they did and in shooting him.
What I always do when I read stories like this is try to learn something from them. In this case, it further reinforces my belief that carrying while in any way impaired is a bad idea. Also, it's made me think more about what I would do if confronted by police and told to put down my holstered gun. I don't understand how Officer Mosher expected him to put his holstered gun down without drawing it. Perhaps the wisest course of action would be to calmly say in a normal voice, "Officer, I can't put my gun down without drawing it, and I'm not willing to draw my gun because it could make you feel unsafe. I would prefer that you disarm me instead. Please tell me how you'd like to proceed." Not that saying anything in any voice would necessarily work when facing officers who feel their lives are in danger and are in condition red or black, though one would hope officers have the training to overcome the stress of the situation and think rationally.
But even there, it seems like the officers had already ordered him to lay on the ground several times, and he hadn't complied. It probably wouldn't have come up if he had done as they ordered and never moved his hand toward his weapon.