Pittsburgh Zoo officials and police were trying to determine what happened after a 2-year-old boy fell into an African painted dog exhibit on Sunday and died before police could save him.
A news conference was scheduled for 10 a.m. Pacific Standard Time on Monday.
Police said the boy's unidentified 34-year-old mother, from Pleasant Hills, Pa., was holding her son over a four-foot railing in an elevated viewing area when he fell. The boy hit and then flipped over a mesh barrier before hitting the ground.
Several of the dogs immediately attacked, and one had to be shot by a police officer. Witnesses estimated the whole event lasted about five minutes, police said.
It's not known if the boy died on impact or if the animals killed him.
Steve Feldman, a spokesman for the Assn. of Zoos and Aquariums, told the Associated Press that it might be the first reported death of a child at an accredited zoo in 40 years.