I decided to do a bit of reading on the topic after seeing the video- it just seemed horrible, and I don't understand how something like that could happen. Unfortunately my experience with the news has often told me that they enjoy sensationalizing everything, especially something race-related.
So my understanding is that the actual big legal question here is whether or not what Slager actions are fitting of the conclusions from Tennessee v. Garner, that is, "did the officer have probable cause to believe that the suspect poses a significant threat of death or serious physical injury to the officer or others"? The knee-jerk reaction I first had on seeing that video was a very strong "no", I mean, the guy was unarmed, and running away.
But Tennessee v. Garner is actually specifically about suspects who are running away. The problem is that there are claims Mr. Scott was struggling for the officer's taser and (supposedly) tried to use it on Officer Slager before trying to run away, which, if true, is actually assault on an officer, which to my knowledge is classified as a felony. Different news sources claim different things (and frankly I don't find any of them particularly reliable when everyone's still upset about it) and this is probably something that will have to be settled in the courtroom.
I think after reading a bit, what scares me more than the fact that this happened is the fact that technically, the officer might've actually been doing something legally justifiable.