I was asked to make a Milton megathread, so that is what I am doing. I'm going to be somewhat busy this evening, so I don't think I'll be able to quickly or easily update the thread with new information, but here are some resources:
From the looks of the video it doesn't necessary look like the dog was tied up, but that maybe it escaped its house/owner and got its leash stuck in the fence. It's still sad, and especially fucked up if the owners left the dog behind, somehow, but I don't want to jump to the conclusion that this happened on purpose until there is further info on it.