Unfortunately, things like this happen. It was sad that such action had to be taken against the tiger, even if they are "tamed" they still have instincts. In this case, the tiger probably felt threatened.
Not all captive animals are kept as pets. Sometimes, animals are rescued from someone who would mistreat them as "pets" and zoos don't always have room. It's hard to rehab once captive animals with animals that are captive from the wild, especially when they've been declawed or something along the lines of that. So they go to someone who is trained to handle them fosters them for rehab. Sometimes, they can't be taken to live at zoos because they have never had a proper habitat or socialization to other animals their type. \
I foster and aquatic turtle and unfortunately, we found we can't reintroduce him to a wildlife habitat. He was diseased when we got him, and we took care of him and his disease is gone, but he's very small and his develpment is weak. He has good socialization skills however, it still hasn't had much of an effect on his development.
It's a sad thing that the tiger was killed, possibly because of some neglect because of the owner. I hope it doesn't reflect badly though, on those who foster or rescue wild animals.
