Tragedy at the pittsburgh zoo on sunday. A 2-year-old boy was killed when he fell into an exhibit of endangered african dogs. His mother put him up on a railing for a look and then the he lost his... See More
Tragedy at the pittsburgh zoo on sunday. A 2-year-old boy was killed when he fell into an exhibit of endangered african dogs. His mother put him up on a railing for a look and then the he lost his balance. Reporter: George, the pittsburgh zoo behind me remains closed indefinitely until this investigation continues. The mother and father of the boy reportedly treated for emotional stress at a local hospital. He fell into a pen of dogs. Experts say he didn't spend a chance. Pittsburgh police are investigating how the toddler could have fallen into the enclosure with african wild dogs like this. Witness say the horrific incident happened five minutes but felt like an eternity. We heard screams and maybe five minutes passed why until we heard what sounded like gunshots. Reporter: It all began noon sunday when police say the mother stood the boy on a wooden rail. But witnesses say the boy lost his balance, falling 14 feet into the exhibit. There's a railing with a graphic sign on the railing and the child slipped over the top of that railing. And there's also a catch basin to catch things that fall into it. But apparently the child slipped over that as well. That's when the dogs, 11 in all, began to maul the toddler. We could hear screaming over the hillside staying "stay away, stay away." As the child's mother screamed the zookeepers came in. The most aggressive animals shot and killed by pittsburgh police but it was too late. From what I understand it occurred at that scene. It was very horrific. Reporter: African painted dogs are an endangered species roughly the size of domestic dogs but they're incredibly aggressive. They are the most aggressive predatory animals in the wild. I don't care if a zookeeper, a policeman, a tranquilizer gun could not have helped. Sorry is not even a word for condolences. Just my heart aches for everybody. Reporter: In may, the dogs caused a lockdown when they escaped to another part of the exhibit. Never before have they been a threat. One of the things the medical examiner is looking at did the boy fall from the impact of the fall or was it the wild dogs. Elizabeth, back to you. Oh, you just hope that he did die on impact. Thank you so much. That's an awful story.
This transcript has been automatically generated and may not be 100% accurate.