Is it illegal for a doorman to maliciously withhold a tenants mail?

I live in NYC and been having problems with a doorman in my building. On occasion, he insists my packages (from UPS or Fed EX) are not there, although the on-line tracking indicates they were signed for and delivered (by another doorman). Finally caught him red-handed (he signed for a package and claimed it wasn't there). I need to know if what he is doing is illegal. I complained to my building manager but she could care less. PS - I do not have such problems with the US postal service as the mailman puts the mail directly in my locked box.