I have an iguana for past 17 years.  I take him outside to catch some rays.  Now if a cat or hawk came and got him in my backyard then I would blame myself for not being by his side to protect him even if it was in my backyard.  I understand the cat owners frustration though because I'd want to kill whatever killed my pet.

Kill the neighbor and move???

Kinding... Just go talk to the neighbor and say that you just discovered that and that your deeply sorry for the dog behavior. And remember that this kind of situation is commonplace between animals.

And I don't think it's remotely acceptable to kill the dog unless he would be a danger to a human being. Because if we go for the "could be" then all humans should be killed because any human can kill another depending on the situation.
And about dogs being tamed... sorry to burst the bubble of guys that have only lived in cities... pick your tamed dog go to a farm and let your dog run free with other dogs and it will most certainly get back with a gift for you, Dogs are hunters through and through.
And loving dogs as I do and if I had a pet cat I also would love it, if another person's dog killed my cat I would be sorry, but knowing the guy probably also loves his dog I wouldn't demand the termination of the cat. The dog doesn't rationalize and sometimes even the most responsible owner may have an oversight...
Killing someone for crimes should be reserved to people (or animals that are really dangerous to people), because they can either know that what they done is wrong or just doesn't care.

Sounds like you & your friend should burden more fault than your neighbour.

However, it certainly is not necessary by all logical means to put down your dog, since it had never demonstrated any aggressive behaviour towards other people or animals, and we never know what happened to have caused it.

Moreover, if a domestic animal kills another animal is condition enough to put it down, then many cats (and perhaps dogs) out there will need to be put down too. I do believe cats are more likely to have killed other animals in their habitat like birds or mice and they certainly aren't suffering consequences for it unless you're living in Australia or countries with similar law reinforcement.

So sorry to hear! Give your pup a good lesson and try make it up for your neighbour.

Don't know you're situation in terms of laws and legislation, so i can't say anything about it.

But the other two points:
Mine is old german herding dog and white shepherd (ironically she's black).

The herding dog basically means she is suspicious about foreign things and always tries to take care of her 'herd' and her pack. And having had some incident with a cat when she was a puppy she doesn't like them in general. But you can get a dog used to things it mistrusts or doesn't like and that's what i'm doing with 'foreign things' as well with cats.

The other side might be that the husky hunting instincts and the need for work both breeds have need some kind of focus and actual work.

Those things are what you should have done and at least should do in the future if it doen't get put down. If you can't handle that it's effectively the wrong pet for you, no offense.

Yeah, it's just not working. We should just put down all cat killing dogs immediately.

If I were you op then I'd move the dog to a friend or family's place. Keeping the dog around might not end well. You already know neighbor wants your dog dead. His blood will probably boil everytime he hears your dog bark or sees him. So if you keep him around it might just push him to take action in his own hands. Who knows? He might drop some tainted meat over the fence or god knows what. I wouldn't put it past anyone. So best idea would probably find your dog a new home (with a good fence where he can't get out again).

I used to manage a municipality. Huskies, it's always huskies. They cause more incidents with other animals than anything else. And you are a lousy husky owner. Your animal should and probably will be put down as it's a killer, and you are not capable of controlling it. If it was my city I would present the option of giving the dog to someone outside the municipality to avoid putting it down, but you would definitely be banned from owning it. Most city managers wouldn't have that option though.

You seem oblivious to the gravity of the situation. Through your own negligence your animal escaped and killed. Contrary to what cartoons tell us, dogs don't naturally hate or hunt cats. They chase any small animal and uncivilized dogs will kill them. You just killed a loved pet with your dog, and it could have been a loved newborn human just as easily.

If my cat was killed by your dog, I would destroy your dog.

Legally it would be your fault and you would have to carry with expenses of anything, what I don't think is that it would mean killing your dog.

My japanese akita has killed 3 cats that were on my backyard, but the key point is that, they were the ones that entered the house. And I think it's to be expected that a dog can kill a cat or a small animal wothout it being considerer dangerous to people at least