I'd make a distinction in your letter between panhandlers and "the criminal element." This is not because your description is wrong--I've lived in Durham and I believe that I've been to that shopping center--but because it provides a likely distraction from your main point.
If a reader's focus is captured by the unproven allegation that the panhandlers are
the same individuals who might rob you, then his/her attention is drawn away from your valid assertion that there
are criminals somewhere nearby. The reason that you're there at all, and carrying, is that customers such as you and your wife cannot know exactly which person hanging around that mall might attack you.
Perhaps you could add a sentence such as the following. After you write in paragraph 4,
Please note that my parking spot was no more than twenty (20) feet from the entrance to your establishment. These events occurred in broad daylight.
you might add, for example,
While panhandling itself is merely a nuisance, those areas that permit agressive, frequent panhandling also provide safe haven for more violent criminals. If your place of business is a comfortable setting in which people can approach your customers and ask for money and cigarettes, then the stage has been set for more violent demands.
Again, you want them to get your message without being distracted by worrying about whether their company will end up in the newspaper, accused of hating poor people, or black people, or local people, or the like. You haven't mentioned the ethnic group of either you and your wife or the panhandlers who approached you. Leave it out; it's irrelevant. What is relevant is that you're authorized by the State of North Carolina to carry concealed handguns, and the store will profit by honoring your permit. All they have to do is to quit making the effort to prohibit you.