Call the police
I highly suggest calling the police and at least putting this on their radar. Then, if he shows up at the park again, you can call them and have them come out. I know that some people think that the police will not do anything, but remember there are Federal laws against animal cruelty and they are taken very seriously. Also, I would suggest contacting your local SPCA office and alerting them. Also, if you see him again let him know that you have made the contacts and that you will be giving the police his license plate number.