Also I counted at least 8 shots, possibly 9 (if the audio has not been edited).
My point is that most likely the gun was empty while the gunman went on his diatribe to the crunched down security team guarding Karlov, among others, with nary a soul charging him. There's even a slight possibility that this was all staged and that old-fart Andrei is now formally retired to live the life of
All these are possibilities, correct. But let's do some actual research.
First off, we need to know the model of gun the assassin used, and the magazine capacity. It would make sense for the assassin to use a full magazine, and I suspect that most modern semi-auto pistols carry more than 8 or 9 rounds in a magazine. I'm absolutley not a gun expert though, just speculating.
I don't really see why it matters whether the gun was empty or not, everyone at the scene would assume that it wasn't, for their own safety.
As for the fact that he wasn't gunned down earlier, eg straight after he pulled his weapon, could be down to poorly trained security, and the fact the meeting was in an unlikely place for an assassination, taking them off guard. Of course, another scenario could be that the security team were paid off, or had ulterior motives and wanted the ambassador killed.
Until more evidence surfaces it makes no sense to speculate about things like "staged assassinations" etc. Of course it's possible, but pretty unlikely at this point.