Again I will ask: Have you read anything from the four days of testimony? If you do, instead of relying on the rhetoric of others, you may gain a different perspective.
If you read about the testimony, you will find that a large number of eyewitnesses stated that he pulled a gun. They did not see a holstered gun. They saw a gun. They believed that Scott was pointing a gun at the officer. Clearly, the officer also thought Scott was pointing an unholstered gun at him.
Under the law (and, if you go armed, I hope you are aware of this), what you reasonably believe, not necessarily the truth of the circumstances, is what matters when you claim justification in a shooting. If you reasonably believe that you are in danger, you may defend yourself, whether or not you really were in danger.
Since so many eyewitnesses have testified that Scott pulled a gun, it would be reasonable for the officer to have seen it that way in the split-second he had to react.
Folks, once again, I implore you to read the summary of all the eyewitness testimony. In one of my above posts, I have provided four links to the daily reports of the testimony. It will change your perception. It changed mine.