I didn't see any rocks in his hand. Are you saying that, after the fact, they get to kill him? Isn't that the same thing as saying, "He tried to stab me but missed. Then he dropped the knife and ran. I still shot him though, because ten minutes ago he tried to stab me"?
So you were there? I hope you're not relying on some phone video, which more than likely didn't capture the whole incident from the beginning. I'm surprised that with all the half-fact reporting, by the media, including comments by so-called bystanders, which are usually turned around once the real facts of the case are reported, that there's still people who have gut reactions to this stuff.
I just viewed the video at the article link, and if you can’t tell that he’s throwing something at the cops, then you need to get your eyes examined. He’d run, stop, turn around, throw the alleged rocks, turn and run again, then stop, turn around and throw another one. It’s pretty clear to me he was throwing rocks at the cops, and refusing to stop.