My neighbor is a drug dealer, what should I do?

I live in a very nice urban neighborhood in the heart of a major city. All the houses in my neighborhood are 1940's bungalows. The community was originally all white, however white flight took effect in the mid 70's and now the community is mostly African American, however since earlier this century, the community has gone through gentrification and now there are a number of white residents that have moved into the neighborhood. The neighborhood is desirable because of it's proximity to Downtown and that residents over the decades has kept the community up. I moved into the neighborhood three years ago and have not experience or observed or heard of any crime at all. On my street, most of the residents are retire senior citizens that are home all day and serve as my security system because they know everybody and seeks out strangers. However on of my elderly neighbors has a great grandson that I am at least 99% sure that sells drugs. He is about 21, does not work, he is home all the time and has no car. I grew up in the rough side of Memphis, Tennessee, so I know the signs of a drug dealer. I see random cars appear, he come out of his basement unit of his great grandmother's house, either gets in the car or goes to the driver window, spend about 2-3 minutes and goes back inside. I have seen this behavior for the past three years. He has a thug appearance, but seems harmless, he is handsome, I notice that he has a young son and a girlfriend that visits frequently. My fear is that one day, a drug deal with go bad and something can happen to his great grandmother, son, or even me since I live directly across the street. I really don't want to get involved. He has never bothered me. I really have no concrete proof, but I am not naive, I lived with drug dealers (my uncle and sister's ex) before and lived amongst others in my neighborhood in Memphis, so I know all the signs, I could become a DEA agent. What do you think I should do?