PITTSBURGH -- The mother of a two-year-old boy who was mauled to death after falling into a zoo exhibit of wild African dogs won't be prosecuted.

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

The boy fell off a railing that 34-year-old Elizabeth Derkosh had put him on top of to view a pack of African painted dogs, and they immediately pounced on the child, who bled to death.

Zappala says witnesses described the boy lunging forward, as if he thought there was some sort of clear barrier to stop him.

Zappala says he's still investigating whether any charges will be filed against the zoo, and what changes need to be made there.