Boy fell into wild dog enclosure at Pittsburgh Zoo after mother lifted him onto railing for a better view

The parents of a two-year-old boy who was mauled to death when he fell into a zoo enclosure which housed 11 African wild dogs are under sedation as they come to terms with the shocking accident.

New evidence is emerging into the events that led up to the horrifying death at the Pittsburgh Zoo yesterday. 

The Pittsburgh Post-Gazette reported police said the mother was attempting to give her son a better look at the ferocious animals when tragedy struck.

It said she lifted her son in a standing position onto the 4-foot-high wooden railing of an elevated, gazebo-like structure which overlooks the wild dog pen.

The toddler lost his footing and toppled over the railing. He then hit a mesh shelf which is in place to catch objects such as cameras and landed on the ground of the enclsoure. 

"It was very horrific," police officer Kevin Kraus told Fox News. 

As the pack of dogs began to attack the boy, zookeepers ran into the enclosure and fired darts to get them away from the boy but "unfortunately, the dogs were in pack mentality and not responding."

Officials said in a statement a police officer killed one "aggressive" dog with a gunshot because it refused to move away from the child.

Witnesses spoke of the horror of the attack which lasted five minutes but felt much longer.

"We heard screams pretty loudly, and maybe like five minutes had passed by before we heard of what sounded like gunshots," Carey Lenz told ABC News.

Authorities have not released the boy's name. His mother, 34, who lives just outside Pittsburgh, was comforted by her husband who rushed to the scene. The mother and son were at the zoo with relatives on a family outing.

AP reported police and zoo officials were trying to determine if the boy died as a result of the 14 feet fall or from the attack. 

"It's clear that the dogs did attack the child, but whether he died of the attack or the fall has yet to be determined," Zoo President and CEO, Barbara Baker, said.

African wild dogs, an endangered species, are about as big as medium-sized domestic dogs, and weigh up to 80 pounds, according to the zoo.

A number of investigations, both internal and external, are under way into the tragedy. 

It is not the first incident involving the dogs at the zoo. In May, nine of the 11 painted dogs escaped a section of their enclosure, causing a brief shutdown of the zoo. No one was injured, NBC reported.

The zoo was evacuated following today's attack and remains closed indefinitely.

Baker said in a statement: "Our hearts and prayers and deepest sympathies go out to the family of the child."