Who can i report to if i found out my old landlord is living and renting the house that is not his?

my old landlord is living and renting rooms out in the house that dont even belong to him.It belongs to an old woman who is in a nursing home and is senile and have no kids. He is even using her cheques to buy things for himself and her bank account to pay for stuff.He is even putting ads online to try sell both the old woman's car in the garage. Where can i report this to if the house is located in the bronx?