The investigation in the days following the tiger incident turned up at least one reliable witness at the zoo who witnessed the young men taunting the lions and the tigers, and shooting at them with sling shots. The men were old enough to know better. They also found an empty vodka bottle in the (underage) men's car. So they played a large part in their own death/injury.
The zoo, too, is responsible, as the enclosure wall was 4 feet lower than is mandated for safety with an animal of that size and nature.
The tiger was defending itself and acting in a normal manner for a wild animal. And whereas I know animals and humans are different, the animal this time clearly got the short end of the deal.