I am angry, disappointed and sad to read the report on May 30 ("Gorilla shot dead after 4-year-old falls into enclosure").

I am shocked that, as advanced as the United States is, it hasn't seemed to have created instant tranquillizers that the zoo could have used, instead of shooting the gorilla dead.

I wonder if the 17-year-old gorilla, Harambe, was merely playing with and protecting the four-year-old boy, as well as trying to take him out of the enclosure ("Outrage on social media after zoo kills gorilla to save boy"; May 31).

In 1996, at Chicago's Brookfield Zoo, an eight-year-old female gorilla, Binti Jua, rescued a three-year-old boy who had fallen into the primate exhibit ("When animals came to the rescue of man"; Aug 25, 1996). Binti scooped up the unconscious boy and carried him to safety.

At the Singapore Zoo, a cleaner jumped into the white tiger enclosure and was killed by the animals in 2008 ("Cleaner killed by zoo tigers / Victim had been acting strangely"; Nov 14, 2008).

The animals finally backed off the cleaner when a door to the tigers' feeding area was opened, and they retreated to it. But it was too late.

If there had been instant tranquillizers then, perhaps the man may have been saved.

I really hope instant tranquillizers can be readily available soon, to prevent the unnecessary killing of animals and human beings.

Ace Kindredzen Cheong