This is indeed a sad story. The person who euthanized the animal should have been held accountable in some way or fashion. The pain of losing a pet is hard enough when they die naturally and this must have been very hard to bear in light of how it happened.
When I was in Florida, I volunteered at animal control for the town I lived in. I saw dogs put down that had bad diseases and some who were so mean you could not safely get near them. I was on the verge of adopting one such animal. I had been in the pen with her and walked her on a leash many times, but the men who took care of the dogs, there had taken her out in the yard for exercise and out of the blue without warning of any kind this dog attacked one of the men. She had to be put down.
When I came the next day they told me what had happened and they had tears in their eyes for me, knowing I was willing to give the dog a home, and for the dog whom they cared about and they felt really bad about what had happened.
I totally agreed with what they had to do, for this dog became non-adoptable because she could not be trusted. They said her former owner had beaten her from the time she was a puppy. So sometimes as much as we want to save them all it just is not possible.
But when a good loving family pet is killed for no good reason it makes no sense at all.