Wondering if he is the one that is leaving the trash or is it one of his tenants? Either way, he is ultimately responsible, but if it is a tenant, he needs to check his properties more frequently and take care of the trash situation.
He was cited 4 times in 2007, so it can be done. Keep taking pictures and calling Code Enforcement. Keep notes on when you have called and if they have responded. You'll be able to tell by the yellow citation on the door of the residence. If they fail to respond to your calls, call the City Manager's office. If that fails, call one of the TV news stations.