The petition is proof that in this world, there are those that would complain they are on fire, and there are those that would complain that someone is trying to put it out (the latter is usually the ones whom are offended by anything and everything and can be found on the front line of every picket / march on offer).
Its an unfortunate series of events / circumstances that lead to the death of an animal, but if the choice comes down to a human (and an innocent 4 year old child doing what 4 year olds do, climb and explore) or an animal, then the human has to win every time.
Should the parents have paid more attention, perhaps, but having had x2 4 year olds, they are fast little buggers and even the most watchful of parents can't prevent $h1t happening.
Should the enclosure be more secure to prevent a child from entering, almost certainly. Its happened before although I think this was a female gorilla not male and it seemed to obey its command to return to the den
Are either solely to blame or free from blame, no.
Watching the footage, the gorilla seemed confused, dragging the kid through the water like a play thing initially but then he seems to realise that its / hes alive and stands guard over him. Now the footage I've viewed is only a brief (30s) clip and I'm sure there is more there which may show different behaviour.
Its horrible that the call had to be made, but ultimately I think it was the right one