What can I do to help protect my landlord that is severely getting taken advantage of financially? He is 65 and has Parkinson's disease.

my landlord use to have a tenant that lived in his house for 12 years, the amount of money that he has taken off him is forseen!! this man has stolen off of other elderly people, there medication or money, and he is doing it to my landlord. this man is on drugs, i'm not sure which ones, but he has done rehab and didn't finish and what not. this man is in his late 40's early 50's and does not have a job, his job is getting money off my landlord. my landlord is a retired school teacher and had a very decent amount of money in his account, it has been completely wiped out to the point where sometimes his account gets in the negative, i know all this because i am a bank teller and my landlord is a customer at my bank. his account has been pretty much wiped out because of this man. what he has done is the house he was living in that my landlord owns he would say that he was fixing up the house and doing repairs so he wouldn't have to pay full rent or get money from the landlord. but he never fixed anything up in the house or did anything. my landlord would give him money for all sorts of things for the house and he never got it, never showed receits for it or nothing. then about a year ago he finally moved out because his wife inherited a house from her just passed aunt and uncle which by the way they cleared out there bank accounts too which was about 100,000 - 200,000. so after he moved out he was still getting my landlord to right him checks for stuff that he claimed he was doing but not actually doing. this is the kicker out of everything, this man has stolen from my landlords brother!!! he talked his brother into letting this man do work for him at his house, well he found his check book and stole checks and was writhing checks on his account and he had no idea, the brother called the police and was pressing charges but they all came to an agreement that if this man went to rehab the brother would drop the charges, well he went to rehab and then left. my landlord also houses his elderly mother that has altemeyers, it's pretty severe.....this man has come into there home and has stolen money that was hidden off my landlord and his mother. when found out he is told that he is no longer welcome in the house but then a couple days later he is right back in there.....something isn't right, and i'm pretty sure my landlords parkensins disease is contributing to it. there is tons more to what i've told you, but all i know is i can't sit here day after day and let this grimy, drug addict, nonworking man take complete advantage of my caring and sweet elderly landlord!!!! please help and tell me what i can do or what you can do. thank you