http://photographyisnotacrime.com/2013/07/01/california-police-arrest-man-for-video-recording-then-kill-his-dog/
The video will explain everything.
Shows poor police judgement. If anything, they could've used pepper spray. The one who shot the dog should be fired and all law enforcement involved should be suspended, no pay, the department should make a public apology to the owner of the dog as well as the public for bad judgement. Just think if the roles were turned and a K-9 dog was shot because they thought their lives were in danger.