They should of called in Bill Cosby to sedate it (no harmful intentions, it may have actually happened)
A high glass window should be fixed around the enclosure for everyones safety and pleasure of viewing.
Secondly letting a child wander off at a zoo wouldnt really qualify you to sue if the kid clambered over the rail, if you were there then it most likely wouldnt have happened.
Third to the animal rights groups, zoos are not corporate enterprises (to my understanding) and lots of money goes into housing, entertaining, breeding and feeding the animals. Also a human life is more valuable to the state than a gorilla, and there was simply no time for tranqing the ape due to the fact that it was gettjng agitated , defensive and a sharp prick might just really tick it off and having a dead gorilla and child would really hurt the zoos reputation, and lawsuits means less money for ensuring the animals have a comfortable life.
That is just my 2c on the arguement. It is sad yes and many parties can be blamed but more importantly it must be avoided in future