It is my understanding that the gorilla did not man handle the child at all. I read (wasn't there) that the gorilla tried to help the boy stand up at one point, and was acting very protective of the child. He became agitated by the screams of the onlookers, so he took the child to another area, but was still protecting the child and not acting aggressively towards it. The only reason they shot it vs. tranq is because tranq's take a bit to kick in, and in a drowsy state like that they didn't want tragedy to happen, as in the gorilla falling over on the child or the gorilla losing its mind in a semi-conscious state. Sad story, but probably the right call. Once again, through the actions of over-entitled humans another animal and effort to study said animal suffers, and I bet that the parents will still have the audacity to sue. That's the true tragedy here IMO, the continuing support of the notion that someone else is always responsible, and you should so whoever you feel that person may be without looking at your own actions.
Sorry if what I post above is either summarized in the article above or contradictory, I tend not to open links from fox news, I read this story originally through a reddit link.
Not threatening but terrifying, expecially with the resistance the water would cause against the child I am surprised his arm was not removed.