Then it's your uncles fault. 1 week to rehome a dog isn't nearly long enough before resorting to a pound.
And rehoming for this is honestly crazy.
I get it, and it was your uncles dog so I'm not blaming you-
My ducks are more than pets to me, I hatched them, I raised them, I have very strong bonds with them, even stronger than the bonds I have with my dogs. But if my dog accidently got in with them and killed them? I'd be distraught. I'd be utterly distraught. But I would not blame my dog. I'd be so hurt, yes, but I'd never ship her off or send her to her death.
When we take an animal in, an animal domesticated and descended from literal wolves, we are committing to the needs of that animal. And that animal has a nature that we can't exactly change. There is no guarantee that this dog will behave in the exact way we want, there's no guarantee they'll never kill a small animal. They may take out a garden bird, a mouse, or a rabbit. Or our own pets. I think it is shocking to kill your own dog because they follow their nature. We should be smart enough to keep them separated, and to train the dog as a preventative. Because we should expect problems when a predatory animal comes into contact with a prey animal.
It's up to us to keep them separate, it's up to us to train them. It's not about which animal we think is worth more, it's about being responsible with all animals that we bring into our homes.
The myth that dogs become blood thirsty after killing once, is just that- a myth. They can be retrained. A dog deserves an owner who will actually dedicate themselves to their care and training.