Three baby squirrels, a rabbit and a ferret were killed as a result of the fire, according to a release from the Humane Society of the United States.
The release also stated that the Humane Society is offering a $2,500 reward for information on anyone involved in the fire.
The fire caused more than $10,000 damage. Fire Marshal Caprice Mellon said the fire was set intentionally and the matter is under further investigation.
The release stated that the fire was caused by the explosion of a 20-pound propane tank. Four of the animals died immediately in the explosion and one squirrel died a few days later.
No humans were hurt, although Assistant General Manager Bart Willis was alone in the building at the time of the fire.
Mondy Lamb, director of public relations for the Wake County Society for the Prevention of Cruelty to Animals, said the group is offering a reward of $1,000 to anyone with "any information that will find anyone responsible for the fire."
Lamb said the reward money that is being offered comes from a fund established by the nonprofit organization for investigation into animal cruelty. The fund is named after a former victim of animal abuse, she said.
"We have what's known as a Buster Award Fund," Lamb said. "Buster was a dog that was horribly abused and lived to tell the tale. Some people specifically earmark money for cruelty investigation. This is the first time we've had to use these funds in this manner."
Lamb also said the Wake County SPCA is also offering emotional help to the shelter.