How to deal with Drug Dealer Neighbors

[Kevin Williams`]

Hello BP, 

I own a property in a quiet neighborhood in Baltimore. The block is filled with working class owners and students...save for one house that has been the eye sore of the neighborhood. These tenants are constantly yelling and having issues, have random people knocking on their doors late at night and littering/loitering. In addition, multiple neighbors have seen these people doing drug transactions around the house, with many different vehicles and I have solid evidence on my surveillance system of drug activity. The issues stems from a long term tenant, of course who doesn't work or respect the property or the neighborhood.

I am unsure of how to handle this as I am a relatively new landlord and don't want my tenants to be involved/put in harms way. 

How have you pros handled this situation in the past? Go to their landlord (*slumlord)? Call the police?

Thank you in advanced for the help!