The 2-year-old boy mauled by African painted dogs Sunday fell over the railing on which his mother put him to view the wild animals at the Pittsburgh Zoo, police said.
The boy died after falling 14 feet into the exhibit, said Barbara Baker, director of the Pittsburgh Zoo & PPG Aquarium. Barker said it's unclear whether the boy died from the fall or from the attack.
Zoo officials tried firing darts to scare the dogs away from the child, but the animals, which are pack hunters, did not immediately respond.
The dogs were eventually moved from the exhibit, with the exception of one, which had to be shot after it continued to "be aggressive" to the boy, Baker told a news conference Sunday.
"Unfortunately, by the time EMTs were able to get to him, the boy had passed away," Baker said.
The boy and his mother, 34, Pleasant Hills, Pa., residents who have not been identified, were visiting the zoo just before noon when police say the toddler's mother stood the boy on a wooden railing outside the exhibit. Witnesses say the boy lost his balance and fell into the exhibit.
"There is a railing with a graphic sign. And the child flipped over the top of that railing, and there is also a catch basin to catch things that fall into the exhibit. But apparently the child flipped over that as well," Barker said.
That's when all 11 dogs pounced on the toddler and began to maul him. Witnesses said the scene lasted five minutes, but felt like an eternity.
"We heard screams pretty loudly, and maybe like five minutes had passed by before we heard of what sounded like gunshots," eyewitness Carey Lenz said.
Zookeepers ran into the enclosure, luring seven of the dogs away. Other zoo officials tried to beat the remaining dogs back. The most aggressive dog was shot and killed by a Pittsburgh police officer.
"From what I have heard, this was a pretty horrific scene," police Lt. Kevin Kraus said.
Police said the boy's father arrived on the scene soon after the accident, according The Associated Press.
The zoo has been closed until further notice.
African painted dogs are an endangered species and are about the size of a medium-sized domestic dog, according to the zoo. African wild dogs are also known as cape hunting dogs, spotted dogs and painted wolves. They have large, rounded ears and dark brown circles around their eyes.
"They are one of the most aggressive predatory animals in the wild. A zookeeper, a tranquilizer gun could not have helped," said Jack Hanna, Columbus Zoo director emeritus.
The Pittsburgh Zoo has raised these dogs since birth, but it's not the first time they've caused trouble. The dogs caused a brief lockdown of the zoo in May after they crawled under a fence to another part of the exhibit. But they never left the exhibit and no one was harmed.
Baker said the Pittsburgh Zoo has never had a visitor death. She said no decision has been made yet about the future of the exhibit.
The Associated Press contributed to this report.