It is standard procedure to kill any 'wild' animal that kills a human to prevent further attacks. The zoo is at fault for not proactively stopping the tiger from getting out, but I would agree with the idea of killing the animal to save other people's life.
The tiger's family? I think you mean the victim's family. I'm sure they will sue the zoo and get a nice settlement.
In context of the question posed, yes, shooting the tiger was the right thing to do. The zoo staff should be trained for these instances and should have tranquilizer darts, but they didn't. As a result, the police had to shoot the tiger to protect the lives of other people, including themselves and the zoo staff.
Serge, I was reminded of this Bad Religion line when I read your first post:
"Hey sister bleeding heart with all of your compassion,
Your labors soothe the hurt but cant assuage temptation."
Granted, you aren't a female, but I hope you get the point.
Most zoos do not soley exist for people's amusement. Zoos exist for animal research, habitat research, conservation, and reproduction of endangered or threatened species. Surely, the animals 'in cages' should be treated humanely, but to deny the existence of zoos because you see them as amusement (and nothing more) is ignorant. Even Animal Safaris here in the states have walls around them. So maybe the question should be, how big of an enclosed habitat should these animals get? How is it that a safari/animal kingdom is ok but a zoo isn't? There are certainly many factors researched when building an animal enclosure, and most of them have to do with the animal's health and well-being.