Elizabeth Derkosh, 33, of Whitehall had been holding her 2-year-old son Maddox on a railing atop the observation area of the African painted dogs exhibit at the Pittsburgh Zoo & PPG Aquarium Nov. 4 when he leaned forward and fell about 14 feet into the exhibit where he was attacked by several of the animals.
Allegheny County District Attorney Stephen Zappala Jr. said Wednesday was "a tragic accident," the Pittsburgh Tribune-Review reported.
"I've heard explanations of how the child fell," Zappala said. "It's probable that this child thought there was Plexiglas where there was not Plexiglas. Witnesses described [the fall] as lunging."
The prosecutor said his office was reviewing whether criminal charges should be brought against the zoo.
The Pittsburgh Post-Gazette reported Zappala said his office was working with city police, the U.S. Department of Agriculture and other agencies to examine the zoo's facilities and procedures.
"We're going to try to ensure that this never occurs again," he said.
There was no surveillance tape of the attack.
Zappala said the mother had to be held back from trying to rescue her son, who was the first patron to be killed at the zoo in its 114-year history.
The dogs have been placed in quarantine for 30 days and zoo President Barbara Baker said there were no plans to reopen the exhibit.