(CNN) -- It happened in seconds. A 2-year-old boy slipped over a railing, bounced into a safety net, bounced again, and tumbled into an exhibit of African painted dogs, which mauled him to death.
The heartbreaking scenario came to light Monday as the Pittsburgh Zoo released details of the child's death Sunday.
If someone had jumped in to save him, would it have helped? "In my professional opinion, no," zoo President Barbara Baker, a veterinarian, said at a news conference today. "There were 11 dogs in the exhibit."
Although there were zoo officials within feet of the exhibit, and others rushed to the scene, it was too late -- it was clear the child was dead, Baker said. "There was no reason to send our staff into harm's way" at that point, she said.
An emergency weapons team and the police arrived. The dogs were moved to another area and are now quarantined. But one dog refused to leave. The police needed to access the scene so, with the zoo's approval, two officers opened fire, killing the remaining dog.
The medical examiner found that the little boy did not die from the fall, Baker said.
Railings throughout the zoo are designed to make it difficult to place children on them, Baker said. They're at a 45-degree angle so that if a child is placed on one and falls, he or she would hopefully fall backward, away from the animal enclosure, she said.
Pittsburgh police say the child was with his 34-year-old mother when he fell from the top of a platform railing and "was immediately attacked by eleven dogs inside the pen."
"Homicide investigators have interviewed several witnesses and zoo personnel, and the investigation is ongoing," police said in a written statement.
Asked whether the zoo takes responsibility for not creating a fail-proof system, Baker responded, "We do everything we possibly can," and "we evaluate it every single day." There is "no such thing as a fail-proof exhibit," she said.
The Association of Zoos and Aquariums will require a report from the zoo, and if it deems necessary, will send an investigative team, Baker said.
All the dogs had physicals in September, which include rabies shots, she said.
The U.S. Department of Agriculture inspected the zoo in September and found no deficiencies, she said. The agency, by law, will return for a follow-up inspection.
Baker did not say whether or how procedures may change as a result of the accident. The zoo has never faced this kind of tragedy, she said.
The zoo will reopen tomorrow, but the African painted dogs exhibit is closed until further notice.
The child has not been identified, and his family has made no public statement.
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