Discussing/examining this elsewhere, I'll note that the officer had already discharged the taser at/into Mr. Scott, and presumably angle/normal clothing prevent a circuit. So when shooting Mr. Scott, he should have known that it was a taser that had been reduced to not only a contact hazard only, but that chance movement could have Mr. Scott tasing himself if the barbs happen to make the right contact.
I also didn't really a struggle. It looked to me that the officer tried to tase Mr. Scott, then practically chucked the taser to the ground, drawing his firearm as Mr. Scott ran. 5 out of 8 shots into Mr. Scott later, all into the back.
Given his initial story of the struggle, how the heck was he planning to justify 5 shots into the back, at a distance? Or is he being tossed under the bus due to the video, while the police wouldn't have bothered to look too closely if it hadn't surfaced?
I'm not saying that Mr. Scott shouldn't have faced consequences for running away from an officer, but that's where you call for more officers and sort things out. Not shoot a non-threatening running man in the back.