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.