All of this is IMO- I agree that she may have been attacked from behind and that's when she released her grip on the leash. Bowie was probably injured after that, and collapsed away where he was found. Also, IMO -If there were any additional acts of violence on Katherine, it was probably post...
The light on the hat bothers me. Could be blinding if you are looking straight at someone. However, I'm told it's common to wear lights on your head.
I think everyone is a suspect if you're on that video.
I feel this is too big of a leap from animal torture. He took on the dog and her all at once. There must be other victims some where, just not in Atlanta or maybe they survived other similar attacks.