Christ. Pretty solid police work, then. Let's just hope whoever sent the order to start lobbing tear gas gets fired for it.
They won't. During the Oakland riots a couple years back, a former Marine was hit in the head with a tear gas canister, shattering his skull. When protesters moved to aid him, a police officer -- caught on film -- through a tear gas grenade at them. He actually was fired...and then reinstated not long after.
Did I mention that said officer has three fatal shootings to his name? There've been many investigations by press in the US, and effectively police can quite literally get away with murder; if they kill someone, no matter how dubious the circumstances, the odds of it being ruled justifiable homicide are somewhere north of 99%.
http://blog.sfgate.com/crime/2014/08/01/scott-olsen-responds-to-rehiring-of-oakland-cop/
There was a really thorough investigation by a Florida paper a few years ago on the matter...I'll see if I can dig it up.