Cincinnati - When a 181kg gorilla grabbed a 3-year-old boy at the Cincinnati Zoo, the sharpshooter who killed the ape wasn't from the police. Instead, the shooter was a specially trained zoo staffer on one of the many dangerous-animal emergency squads at animal parks nationwide.The teams train at firing ranges, stash rifles and shotguns around the grounds and rank the most hazardous species in their care. Members train in elaborate drills for situations like what unfolded in Cincinnati when the child fell into the gorilla's enclosure on Saturday. The staffer who fired hasn't been publicly identified.Created outrageIt's a weighty commitment for people who work among animals they might one day have to kill. But team members understand the need to do it if a human life is in danger."We all know that every day we go to work we're responsible for the safety of not only the animals in our care, but our co-workers and the visiting public," said Denise Wagner, a member of the response team at the Phoenix Zoo, where she's a senior primate keeper focused on orangutans. "We take that responsibility very seriously."The Cincinnati gorilla's death has created outrage over the vigilance of both the zoo and the child's mother. But it also highlighted the unusual work of zoos' homegrown emergency-response teams.The federal Animal Welfare Act, which regulates zoos, doesn't require such teams. But many animal parks establish them as part of gaining accreditation.The roughly 30-member team of zookeepers and operations staffers hasn't had to respond to an actual emergency in at least 12 years, Wagner said. But members regularly serve as extra protection when a "code red" animal - the most dangerous species, such as big cats - is going to the veterinarian after being tranquillised.Danger to boyWhen to shoot comes down to whether an animal is a danger to someone, whether it's moving toward the zoo's boundaries and whether it could be stopped by a tranquilliser, said Bill Zeigler, a senior vice president. Zoos also tell dangerous-animal teams to consider whether they can fire without hitting other people.The Cincinnati Zoo has said tranquilliser wouldn't have worked quickly enough to end the danger to the boy, who suffered scrapes but was rescued.To People for the Ethical Treatment of Animals, the fact that zoos feel the need for sharpshooting teams "is yet more proof of how dangerous and unnatural a captive environment is for animals," said Brittany Peet, a deputy director of the animal rights group's foundation.Zoos emphasise that killing an animal is a last resort.