If the zoo was near closing time when the animal attack occurred the questions that cross my mind and that have not been explored are:
*Who were the keepers assigned to the string that included the Lion House/Tiger Grotto?
*Was the zoo on minimal staff scheduling due to the holiday?
*What time were the cats scheduled to come in and where were the keepers at the time of the incident?
There is a lot of focus on the statement that the door was closed and that could not have been the reason the cat got out but that is often how animals do escape…human error.