There’s another point I was reminded of by a poster in this thread: http://boards.straightdope.com/sdmb/showthread.php?p=11078017#post11078017
Obviously, we don’t know whether that’s the case or not yet; however, this wouldn’t be the first time that has been demonstrated (or used as an excuse–it’s admittedly hard to tell). Those from the Bay Area surely remember the uproar just a few months ago over an officer who shot someone on Bart, who used the “I thought it was a taser” defense.
I don’t know how often this has occurred, Thalion seems to believe it’s happened a few times. All I know is that it’s good deal more difficult to mistake a club or pepper spray with a gun than it is a taser.