Keith Srakocic / AP

The overlook platform where a boy fell into the exhibit home to African painted dogs is seen at the Pittsburgh Zoo on Nov. 5, 2012.

The fatal mauling of a toddler by African wild dogs at the Pittsburgh Zoo highlights an uncomfortable truth for all zoos: No exhibit is fail-proof.

Striking a balance between providing a safe and yet authentic experience is an evolving science on its own, with the ultimate goal being to protect both animals and visitors, said Doug Warmolts, Director of Animal Care at the Columbus Zoo and Aquarium. 

“Short of putting everything behind glass and solid barriers, it’s hard to make everything absolutely safe,” Warmolts said. “People’s expectations when they come to a zoo or aquarium are to have a meaningful experience where they have that connection with the animals, and it’s hard to do that if they’re looking through a chain-link fence.”

Gene J. Puskar / AP file

An African Painted Dog yawns at the Pittsburgh Zoo and Aquarium in Pittsburgh as he lays in a pile of hay Thursday, March 12, 2009.

Maddock Derkosh, 2, fell into an African painted dog exhibit late Sunday morning at the Pittsburgh Zoo & PPG Aquarium. The boy’s mother had put him on a wooden railing at the edge of a viewing deck to see the animals, officials said, and the boy fell into the exhibit. He initially landed on the netting below the deck but bounced several times before dropping about 11 feet into the dog’s enclosure.  

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Witnesses said at least three dogs surrounded quickly, attacking him at his head, neck and legs. An autopsy revealed Monday that the boy was killed by the animals, not by the fall.

The exhibit housing the wild dogs remained closed Tuesday pending an investigation by police, who said it was still too early to determine whether criminal charges will be brought against the zoo or the boy’s mother. The zoo opened for visitors Tuesday.

Accredited by the Association of Zoos & Aquariums in September – the gold standard for zoos in the U.S. – the zoo met or exceeded all safety standards for animals and visitors, Mary Baker, the zoo’s president and CEO, said Monday.

Warmolts said exhibits at accredited zoos are designed by architecture, engineering and design firms that understand zoo animals’ behavior, from their abilities to jump, climb and dig to how to properly care and set standards for them in a zoo setting.

“We have to blend those together to create an exhibit that’s not only a suitable and enriching environment for the animals and a safe experience for people to feel immersed into that environment,” Warmolts said.

“We have fences and barriers and moats and signs and even zoo staff that can keep visitors at a certain distance from the animals. That’s why what happened is very rare. But we can’t always monitor them," he said.

In San Diego, officials said the incident in Pittsburgh is likely to prompt larger, industry-wide reassessments.

“The way humans interact with animals has changed drastically over the last hundred years, so certainly one of the things that zoos have had to be is highly adaptive, especially in these situations when tragic accidents happen,” Christina Simmons, a spokesperson for the San Diego Zoo, told NBC News.

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In Chicago, officials at the Brookfield Zoo said Monday that the events at the Pittsburgh Zoo have so far not prompted the change of any of their practices or protocols.

"We have, like all other accredited institutions, procedures and policies that we follow in the event of an accident -- even a person having a heart attack -- and we also drill on those events too," said Bill Zeigler, the Brookfield Zoo's Senior Vice President of Collections and Animal Programs. 

Even with safety standards enforced, Wamolts said, the zoo industry is constantly dealing with "human error" by its visitors. 

"What happened is very rare," Warmolts said. "We’re always in the process of evaluating and reviewing and making adjustments as needed, and it’s an art to try and determine how to do that. What’s more common is people exhibiting inappropriate behavior. It’s just unfortunate."

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A medical examiner has ruled that a 2-year-old boy who tumbled into an African painted dog exhibit at a Pittsburgh zoo was killed by the animals and not by the fall, a zoo official said Monday.

"What we understand from the medical examiner's report, the child did not die from the fall. The child was mauled by the dogs," said Barbara Baker, CEO and president of the Pittsburgh Zoo and PPG Aquarium, WPIX-TV reported.

Officials say the child's mother had placed the boy on a wooden rail above the exhibit so he could get a better look at the animals. There is a net below the rail, but Baker says the boy bounced off it and into the enclosure.

"The child initially was caught by the netting. From witness accounts the child was so small that he bounced, then he bounced twice and then bounced into the exhibit," Baker said.

Gene J. Puskar / AP file

An African Painted Dog at the Pittsburgh Zoo and Aquarium in Pittsburgh in 2009.

Baker fought back tears as she discussed the incident during a press conference at the zoo on Monday.

"The zoo feels terrible about this tragic accident that happened. It's your worst nightmare as a zoo professional," Baker said, according to WPIX-TV.

The animals attacked so quickly that by the time a veterinarian and other zoo staffers arrived, they determined it would have been futile to try to rescue the child, Baker said.

Boy falls into Pittsburgh zoo exhibit, mauled to death by African painted dogs

'Someone help!'
Authorities said that zoo staff and then police responded "within minutes." Visitors described that time as being filled with screams for help.

"The screams just kept coming and coming: 'Someone help! Someone has to do something',” Angela Cinti, a witness, told The Pittsburgh Post-Gazette on Sunday.  

Zookeepers called off some of the dogs, and seven of them immediately went to a back building. Three more eventually were drawn away from the child, but the last dog was aggressive and police had to shoot the animal.

"There were three dogs, one at his head, one on the left side of his neck and another one down by his leg, " Cinti told The Post-Gazette. ”A [zoo employee] got there and hopped over a fence with a rake and he was banging ... trying to distract the dogs, but they wouldn't move."

Experts said the death is highly unusual.

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Steve Feldman, a spokesman for the Association of Zoos and Aquariums, told The Associated Press no one he's spoken to can recall any deaths of children at an accredited zoo over the last 40 years or more. Feldman said the Pittsburgh Zoo successfully completed its five-year review in September, which means it meets or exceeds all safety standards.

Authorities didn't release the name of the boy but relatives identified him as Maddock Derkosh, according to the Post-Gazette. Authorities said his mother is 34 years old and lives in Pleasant Hills, just outside Pittsburgh. The boy's father was identified by the Post-Gazette as Jason Derkosh, a building designer at the architectural firm L. Robert Kimball & Associates.

The zoo was immediately closed, and it was not clear when it will reopen, authorities said.

African painted dogs are about as big as medium-sized domestic dogs, and weight 37 to 80 pounds, according to the zoo. They have large, rounded ears and dark brown circles around their eyes and are considered endangered.

The attack happened in a 1.5 acre exhibit called the Painted Dog Bush Camp that's part of a larger open area where elephants, lions and other animals can be seen. Visitors walk onto a deck that is glassed on the sides, but open in front where the roughly four-foot railing is located.

In May, some of the dogs crawled under a fence and escaped into a part of the exhibit that's usually closed. The zoo was on lockdown for about an hour as a precaution and the animals were coaxed back in.

Fatal attacks
Past fatal attacks have prompted zoos around the nation to review safety features of their exhibits. In 2007 a tiger jumped over a wall at the San Francisco Zoo, killing one visitor and wounding two others. Authorities first said the wall was 18 feet high, but a review found it was just 12 ½ feet.

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In September a man jumped off an elevated viewing train at the Bronx Zoo in New York and was severely mauled by tigers.

Kraus said there was nothing to prevent visitors to the Pittsburgh Zoo's painted dog exhibit from jumping into the exhibit area.

Police and the Allegheny County medical examiner's office are investigating, and they haven't yet interviewed the mother or father, who are receiving grief counseling.

Baker said the zoo, which has never had a visitor death, will also investigate. She said no decision has been made yet on the future of the exhibit.

NBC News's Sevil Omer and The Associated Press contributed to this report.

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