It is not clear if the below video shows the incident where the officer was killed but it was an aggressive move.
Here is the thing. The guy throwing the extinguisher is carrying a backpack.
This is a mark of organized protestors.
I have seen plenty of protests in San Francisco and Oakland to know to watch out for the guys carrying backpacks. Out here they are lefty anarchists.
Most people don't carry backpacks to protests. The guys with backpacks are generally much more organized and looking for trouble.
I don't know who the guy is but he fits the profile of someone coming from a radical group that wants to create violent mayhem.