How do I report someone who posed to be my mother's POA when I in fact had a valid POA? She took a bank account that my mother and I had.

This woman posed as my mother's POA fraudulently and took the bank account a joint bank account my mother and I had. It had been at Downey savings and Downey savings going out of business it went to u.s. bank and she posed as POA drained that bank account totally. My mother is deceased, how do I handle this matter.

Although she was not she has written it down on doctor's forms and sent them to my mother's doctor. It's a joint account which eventually she drained totally before my mother came to live with me unbeknownst to me I have it in writing from the woman's own hand. I know she wrote to one of my mother's doctors that I found out later on after my mother came to live with me my mother is deceased how do I recover this money and stop this woman from doing it to someone else sincerely.