I think the circumstances around the accident needs to be known. Just because a dog kills another dog doesn't mean it's dog aggressive. A great Dane could very easy kill a small dog during play. My 85 lb dog could probably run into a puppy the right way and kill it.
This was my thought as well.
What was the situation? I'm going to assume the dog was also stressed about a new home. Curious for more info.
Sad story all around.