PITTSBURGH — Police and the Pittsburgh Zoo and Aquarium are investigating the deadly mauling of a two-year-old boy Sunday. Zoo officials say the child fell over a four-foot high wooden railing and off a mesh barrier into an exhibit with African painted dogs. The zoo says darts were fired to chase off the dogs but they were, quote, “in pack mentality and not responding.” One of the dogs was shot and killed by a Pittsburgh police officer. The “Post-Gazette” reports keepers say they were unable to get to the boy. The boy was from Pleasant Hills and was at the zoo with his mother. The exhibit’s future has not been determined.