Updated

The mother of a 2-year-old boy who was mauled to death after falling into an exhibit of wild African dogs won't be prosecuted, but authorities are still investigating the zoo for possible criminal negligence.

Allegheny County District Attorney Stephen A. Zappala Jr. said Wednesday that Maddox Derkosh's death at the Pittsburgh Zoo was a "tragic accident."

Zappala said the boy had vision problems and wore glasses, and that's partly why his mother, 34-year-old Elizabeth Derkosh, had lifted the boy on a railing to view the pack of African painted dogs in early November. Zappala said witnesses described the boy lunging forward, as if he thought there was some sort of clear barrier to stop him. The boy fell and the animals immediately pounced on the child, who bled to death.

Zappala said he's concerned about an internal zoo memo from October that Pittsburgh station KDKA obtained, stating that there would be no security guard at the zoo from 7 a.m. to 3 p.m. during weekdays. Derkosh died during a weekend, but Zappala said the investigation is continuing, and will review whether the zoo was guilty of criminal negligence or endangering the welfare of children, and what changes need to be made to prevent future accidents.

Zoo president Barbara Baker told The Associated Press that when the tragedy happened the zoo was fully staffed, including security.

"Our thoughts and prayers still go out to the family," Baker said, adding that the zoo is cooperating with all investigations.

An internal zoo review is continuing, Baker said.