1) Report the incident to the authorities.
2) ASAP after step 1: Notify the store manager as well as Petsmart corporate, along with the police report. Make it evident that you will cause an uproar. Petsmart will want to protect their reputation, and he will be fired in short order.
3) Follow up with the authorities to make sure they do their job. Repeat step 3 as much as necessary.