Yeah, that's happened repeatedly. They'll do it right in front of the owners too, and if they're ever questioned about it they'll simply say the dog was vicious and charged him, and that he feared for his life.
Or sometimes they won't even bother with trying to set up a fake aggressive charge scenario. Been a number of cases where someone was standing there talking to the officer, the dog's on leash and doing nothing, then suddenly BANG! One I remember was a gal with her GSD at her side, the dog had a rawhide and was doing that typical happy I-got-a-toy thing of rolling it around in his mouth. The cop claimed the dog "bared its teeth" at him. More likely it was the cop's way of saying not to bother him with stupid shit he doesn't care about. Another that comes to mind was a guy with his elderly golden retriever, which was shot with the claim that it was an aggressive pitbull.