The barrier around a gorilla exhibit at the Cincinnati Zoo was not in compliance with regulations when a 3-year-old boy fell into the enclosure in May, according to a federal investigation.

Zoo officials questioned the finding by pointing out the barrier passed muster with federal authorities about a month before the boys fall.

In its 38-year history, the barrier system at Gorilla World has always been found compliant during USDA inspections, a statement from the zoo said.

A member of an animal response team fatally shot a Western lowland gorilla named Harambe on May 28 after determining that the ape posed an imminent threat to the child. The animals death unleashed a public fury that was directed both at the childs mother and at the zoo for its decision to use lethal force.

Inspectors from the U.S. Department of Agriculture said the barrier around the Gorilla World pen didnt meet standards, according to a report first covered by The Associated Press . The report, however, didnt specify what was wrong with the fence, and The Cincinnati Enquirer said the requirements are vague.

It was in compliance until May 28th and then it was found to be not in compliance as it did not restrict public access from the nonhuman primate, a Department of Agriculture spokeswoman told NBC News .