It was human error - siht happens, and I bet he or she is beating themselves up over it.
Killing the creature was the only option. It was a predator, and as somebody has already said, could have caused problems if it escaped the zoo (they can climb!).
NellieMay - "But I don't agree that humans are more important than animals."
I've heard this a lot over the years and I've always found it a ridiculous thing to say/think, particularly as it's usually said when the creature is handsome, as in this case, or has the 'aaah' factor.
What about sewer rats? Are sewer rats as important as humans? Or wasps? Or flies?
Yes it's very sad this handsome animal was shot, but the threat to human life is much much more important.