In a letter to the U.S. Department of Agriculture, the Animal Rights Foundation of Florida criticized the agency's initial report, which cleared the new theme park of wrongdoing in 29 of the deaths. The USDA's findings were released April 22, the same day the park opened.
"Not only does the result of the investigation have the appearance of a whitewash, but the announcement...on the same day as the park's opening is extremely coincidental," said the group's lawyer, Timothy Ross.
A total of 29 animals, including cheetah cubs, otters, and a rhinoceros, died at or en route to the park between September and April. The causes ranged from maternal neglect to fights among animals trying to establish territory or dominance.
Since the report, a 13-year-old hippo died of bacterial pneumonia.
USDA spokesman Jamie Ambrosi said the agency was awaiting a report on the hippo before deciding whether to begin another investigation.
Disney spokeswoman Diane Ledder couldn't be reached for comment Tuesday.