Zoo Knoxville suspects something "sudden and catastrophic" happened in a reptile building to cause the death of 32 reptiles last week, but are still working to figure out the exact cause.

The zoo originally said 33 reptiles died, but Zoo Knoxville CEO Lisa New said Monday the actual count is 32.

So far, they have ruled out food, disease and infection as causes based on the initial necropsy findings from the University of Tennessee College of Veterinary Medicine.

Last Wednesday morning, zoo staffers entered one of the buildings in the zoo's reptile facility to find 30 snakes and one lizard unresponsive. Of the 52 animals housed in the building, 32 died, including three critically endangered species.

A zoo spokeswoman said Monday that examination of the animals' lungs showed some indication that they had been exposed to an irritant. They will be analyzing blood and tissues samples over the next few weeks for more clues as to what happened.

"Zoo officials suspect something sudden and catastrophic occurred inside the building to alter the environment," Tina Rolen, Zoo Knoxville spokeswoman, said Monday.

During an interview on WBIR's Live at Five at Four Monday, New said the veterinary staff took blood from the animals that died, the animals that survived and reptiles that are houses in other buildings, and will compare those results as they continue looking for the cause.

New said they don't believe the incident was the cause of foul-play.

"It's still a lot of unknowns," she said. "We may not be able to replicate what happened that night. And, of course, there were survivors in the building as well."

Rolen said the building was tested for carbon monoxide, carbon dioxide, methane gas, natural gas and Freon the day the animals were discovered, and none were detected. The building was sealed and tested again on Friday, and no detectable levels were found during the second test, Rolen said.

Rolen said they have also tested the building's temperature monitoring system, which sends out an alarm call if the building's temperature falls outside of an acceptable range, and found that the system is working properly. She said one thermostat was malfunctioning, but monitoring systems show that there was no alert that temperatures went outside the accepted range during the night of the incident.

"Strong thunderstorms were recorded that night, although there was no evidence of power loss or a lightning strike, and the animal housing was not conductive to electricity. There is nothing to indicate the deaths are directly related to the weather," Rolen said.

The building remains out of use while the zoo continues to investigate what happened. The zoo has four other buildings that house reptiles. Those buildings were not affected, and they remain open to the public.

"The rest of the animals are on view and happy and healthy, and in fact, the survivors of the event appear healthy at this point," New said.