Unpaid Rent from a Previous Tenant

[Tim Roberts]

I recently received a check in the mail from a tenant that moved out three months before their lease expired. Shortly after cashing the check the previous tenant texted me and said they were going to sue me for stealing money from their account. It appears the check was sent from a third party online payment processing center (which they set up evidently by mistake).  Lastly, when the tenant moved out I kept their security deposit to cover some of lost rent but they still had a balance owed to me(more than the security deposit and this recent check). What should I do with the money keep it or send it back?