I reread your message, saw you said it was a chain. Call the corporate or customer service number. Relay the incident, mention the people by name if you caught their names.

I've done this with both Petco and Petsmart. If a complaint goes to corporate, it reflects really badly on their store and they will correct it. Hopefully you can get the employee fired, especially if you filed an animal cruelty complaint as well (and be sure to mention this too if you call customer service, which I hope you do).