I'm so sorry this happened to your mother. It is scary when these slick thieves succeed; & not knowing what they may know about you.
Consider the senior mailing lists out there, these thieves can get lists of just the elderly; perhaps by saying they are offering Medicare part D insurance, etc. When we moved to our current home 10 years ago, the people who moved out were seniors. Ever since, I get junk mail targeted to seniors, at first generic, but now in our names. We are not yet seniors, but I have been getting a few more scam phone calls recently & I wonder if this is the reason.
Another thing to stop doing is giving to every charity that sends something to you in the mail, or comes to the door...as my mother does. She is now on every mailing & call list imaginable. I tell her just to donate through church, as she is part of the committee who chooses where they will give. If she did this, she could save herself a lot of junk mail & stop some of these phone solicitations!
Hope the police can help you perhaps through your bank or phone records tracking.