Pittsburgh police Major Crimes Lt. Kevin Kraus said the boy's 34-year-old mother placed the child in a standing position on a wooden railing overlooking the enclosure.
Zoo President and Chief Executive Officer
Barbara Baker said at a news conference shortly after the incident that the child fell over the wooden railing and off of a mesh barrier where the painted dogs were on display. A zoo spokeswoman and police said the wooden railing is 4 feet in height and the lower mesh barrier is 11 feet 4 inches above the open exhibit space.

Lt. Kraus said zoo personnel responded within minutes. The first personnel on scene were able to lure seven of the dogs away from the victim and into a secure and separated area. Lt. Kraus said none of the people who observed the child fall into the enclosure made an attempt to go after him. The news release from zoo officials noted that keepers attempted to enter the yard but were unable to reach the child.
One ineffective technique used by zoo personnel to lure the animals away from the child was to fire "dummy tranquilizer rounds," Lt. Kraus said.
Information released from the zoo indicated that "unfortunately, the dogs were in pack mentality and not responding."
The child was pronounced dead at the scene 12 p.m.
The incident is under investigation by police and the zoo. Police said the boy and his mother are from Pleasant Hills and were visiting the zoo with relatives, an adult and another child, at the time of the incident.
The screams continued.
As they reached the painted dog exhibit, she saw a small crowd of distressed onlookers. Bart DePasquale, who was at the zoo today with his two children for a birthday party, was near the tiger exhibit when he heard screams coming from the direction of the African painted dogs exhibit.
"The screams sounded heavily distressed and the people were using profanity. They were shouting to zoo employees."
Then we were told it was an incident with the wild dogs and that a child had been hurt."
Ms. Baker said the zoo initially declared a "code blue," meaning an accident involving a human had occurred. The African painted dog exhibit debuted after the October 2009 birth of the pups. In the spring of this year, nine of the 11 painted dogs escaped a section of their enclosure causing a brief shutdown of the zoo.
Ms. Baker said at that time on May 5 that the dogs got into a 1.5-acre "backup yard" not visible to the public, but the dogs were not out of their exhibit.
African painted dogs are an endangered species.
In September, the zoo announced that it had again been accredited by the Association of Zoos & Aquariums after a review of its animal care, veterinary programs, conservation, education and safety.
AZA is a nonprofit organization with a team of professionals that inspect and review each zoo or aquarium seeking accreditation. The Pittsburgh zoo has been recognized by AZA since 1986.The accreditation commission evaluates every zoo and aquarium to determine if they meet accepted standards for safety policies and procedures, security, physical facilities, animal management and care, health and nutrition, veterinary programs, involvement in conservation and research and education programs.