I put this out there in hopes that this will not happen to another family.
My aunt became a co-signer on her 92 year old father's bank account. She has essentially taken everything he has ($250,000), ran up credit cards (also a co-signer), let his lights, water and trash service be disconnected. His property taxes went unpaid for two years and were due to be auctioned off - all without his knowledge because she had the mail re-routed so that he would not know. We met with the police and essentially, because she is a co-signer, they say that there is nothing anyone can do. It is her money by way of being a co-owner.
Understand what making someone a joint signer means. The POA is bad enough...but the joint signer is what made it legal. She's figure out the perfect crime and is walking away scott free. He on the other hand is probably going to have to file bankruptcy and will lose his house as he can't afford the credit card payoff.
Sad state of affairs when the law protects the criminals. :(