Oh my goodness! I couldn't disagree more Vintage Boxers. There are lots of dogs that might kill a dog, would kill a dog if given a chance. Dogs are animals and they have their own set of rules and reasons why they do things. This wasn't a human that was attacked. This can be prevented in the future by using a muzzle or leash, a secure fence....utmost care. I wouldn't like to have to worry about that, but lots of people do all the time. People with Pit bulls have to be really careful, for one.
I knew some people with 5 Irish Wolfhounds on their acreage, which had a pretty good fence around it. But a little stray dog came in and their dogs killed that little dog...very sad. No one knew who it belonged to. But that is what dogs do sometimes, especially that type of dog. That sort of drive is what they were selected for.
Toker, for an example, is not one iota dog or human aggressive....loves every person, every dog she ever meets. She is so glad if a dog comes on our property. Woo hoooo...someone to play with. I've never seen her go after another dog ever. The only time she's shown a little warning snarkiness is with food. But she never has bitten one of the other dogs in my household. She adores them, is playful, friendly, snuggly. They all get along fine. Well....to my point: One time, Chulita, one of my Chihuahuas was out in the yard some distance away going pee and I let Toker out of the house. It was dusk, I think and she saw Chuli and didn't realize it was Chuli. She ran after her like she was going to get her...like she would a squirrel or other prey. I yelled, "Toker, no!" (then went on to explain it was Chulita.) LOL. She did listen and then saw that it was Chuli and stopped in her tracks, like, "Oh....it's you." But she could have killed Chulita had she not come to her "senses" in time.
We have to remember that dogs aren't going to be like humans...that they have big, tearing and ripping teeth and jaws, that they have hard wired behaviors, which, for a lot of dogs have become "watered down" sort of...but not for all dogs. We can't just euthanize every dog that doesn't act human enough. We have to manage them, yes. But I don't find that to be such an astronomically abnormal behavior. It isn't that common either, of course because if every dog killed every dog, the species would become extinct. It isn't an every day thing that conspecifics fight to the kill, in other words. But it does happen and with some breeds, it seems to be even more likely.