My dog might have killed our new puppy? (a bit graphic, sorry)

We (now) owne two dogs, a 6-year old Boxer named Duke and a while ago got a Border Collie pup named Cacey. They hit it off pretty well and both enjoyed free roam of a large fenced in yard and access to a lake.

Very recently we got a Samoyed puppy, a female named El. She was only a few months old and not trained yet. We thought the other two were fine with her though. Cacey loved to play with her as they were both pups. Duke seemed more or less indifferent. He liked to run with both but wasn't super tolerant of their puppy antics, such as licking his face. He just moved away, never growled or acted aggressive.

Today, El was found dead in the back of the fenced in yard. She was found by my grandmother who was visiting. She walked around back and found El dead, her face mauled (practically gone.) As she stood there, Duke ran up, grabbed the body and "flung it in the air" according to my grandmother. He didn't act aggressive or anything. She noticed then that Duke was covered in blood, but she couldn't say if he had been bloody before he picked her up.

My step-father ran out and guessed the dog had been dead for about 30 minutes. A worker on the property claimed that Duke had been around them the whole day and hadn't left until our grandmother pulled in and therefore couldn't have done it. Cacey had no blood on him and wasn't in the back, plus he's still young and though he's bigger than El was, he's still puppy in appearance and doesn't seem strong enough or aggressive enough for something like that.

Duke on the otherhand has always been stand-offish and aggressive towards other dogs that he hasn't been introduced to. Once introduced, he's perfectly fine. But he's the type to stand at a fence and bark his head off at passerby dogs. He's never attacked another dog before, though.

Given that Cacey is still a pup and that we have a baby on the way (I'm pregnant and due in less than a month), we don't know what to do with Duke. It appears he must have done it. Is it possible he didn't know what he was doing? Or is it more likely he killed her on purpose?

We don't know and can't know anything for sure. The fenced in area is pretty secure except for a small gap in the back that could let small animals in and out. Certainly nothing big enough to do that to a dog, even a small one, though.

Should we assume it was him, despite not seeing it? Should we do anything different now? Could he have just been playing too roughly, accidentally killed her, or does the extent of the wound seem like aggression?

What would you suggest? I appreciate all input.

I'd suggest you should have been more aware of your puppies whereabouts rather than just leaving them to roam free. How could you be oblivious to what happened. Do I think you're jumping to conclusions? yes massively. I'm also guessing your baby when it arrives won't be left alone with the dogs, that you'll be more attentive so why would it be an issue?

Well, it's difficult to keep an eye on them every minute of every day. There's always at least 3 people on the property who keep an eye on the dogs but it's a big place and sometimes they run around to the back while playing. Seemed better that they have mostly-supervised free-roam than having to sit in cages all day until someone gets home to watch them. Then again, given what happened, maybe not. Honestly, we thought we were doing good by them. I do agree that they they should've been watched better, and I regret that. But your suggestion does little in the way of helping as it's too late to be more aware of a dead pups whereabouts.

As for why it would be an issue later, that's why I'm asking people who might be more knowledgeable about the subject. Is a dog more likely to attack again once it already has? Does an attack on another dog translate to human, despite the dog having never been aggressive to a human? If the attack was prolonged, as it seemed to have been here, does that suggest it was predatory? Or could it also have been the dog accidentally snapped, and then realizing it was dead, considered it a play thing?

They're close family dogs. They run around and play during the day, and then at night they come inside and sleep inside. So there could be points when my toddler is near the dog (though never alone) if allowed.

I'm just looking for advice going forward, especially from anyone who might have experienced anything similar.

It's a worrying time for you. No one can give an answer as we do not know your dog, or what really happened.

Therefore, research behaviourists in your area. Find one who can come out and assess your dogs so that they can give you an educated opinion of the character and temperaments of them so that you have a more informed view of where you go from here

You're right I have never experienced anything similar because I would never allow a young puppy to free roam especially if I couldn't see him. I would build an area for him to have where he would be safe but apart from that puppies need to interact with their humans, they need training. How can anyone tell you what happened if there were 3 adults there and you don't know and we weren't there. How can you possibly know it was a prolonged attack? All I can say is dog on dog aggression is not normally transferred to humans but most people supervise their dogs and train them how to behave around children, they take precautions to keep their child and dogs safe. Your right it's too late for your pup but tbh I would never have put a pup in that situation and at one time I had 7 dogs to supervise and it wasn't that difficult.

That's good advice, we've went ahead and done so. The behaviorist (correctly) told us that it was our fault and for now, to keep Duke separated from Cacey. We'll be scheduling an appointment for him to come out and look at/work with Duke to see where we can go from here.

Thank you!

What you would and would not have done is irrelevant to me at this point. As for the prolonged attack, it's the extent of the puppies wounds that suggest it. It didn't look like a quick snap/accident. The behaviorist we contacted said as much, but agreed that it was impossible to know.

Thank you for your response, however unhelpful it was. Going forward, the trainer recommended that we keep Duke separated from Cacey until he can be evaluated, which we're doing. Hoping for the best going forward, despite our mistakes.

X