Regarding check fraud and impersonation.?

how and where do i report to if i know that my old landlord renting the house that is not his.the owner is an old woman who is senile in a nursing home with no husband or kids.He is using the old woman;s checks for money to pay for his own personal stuff and all. i have the checks and the house ownership to prove that hes not the owner.he even calls some places using the woman's check and act like its her dead husband to pay for things using the check. Where can i report this to, i mean even if i call the police..they just gonna let him go and then im going to be in trouble by this old landlord..hes also trying to sell the cars to people without the car papers and it belongs to the old woman. i wanna know, what charges would he be facing and how and where do i report this to.he is also collecting the rent for the property that he dont own.He lives in the bronx. So pls recommend who exactly i should report this to?