Illegally sold property? HELP

[Isaac Guzman]

So I contacted an owner of a house in my neighborhood. It is boarded up so I figured I'd call and see what she would want for the house. Within a few days there was a sign in the yard with an agents name and a brokerage. So obviously (or so I thought) it had been listed and I lost my chance. 

Interestingly enough, the owner called me a day later and said that she needs help. She said that the people who are selling her house are doing so illegally. She sent me all kinds of paperwork and even a reconveyance letter from 2004 showing the payoff of the house. Additionally, some paperwork she obtained from the city showing some fraudulent paperwork with her and her husband's signature from 2013. However, her husband died in 2008! 

I was very transparent and let her know that I have no clue what to do. When we called the agent who has the listing and inquired as to how she obtained the listing she was speechless and hung up on us. 

There is two reasons I would like to help. (1) The neighborhood has homes ranging from 360K-500K and she agreed to sell it to me for 120K (remember, it's a total gut job).  (2) It is obvious that someone is taking advantage of this widow and I feel convicted to assist in any way I can. 

That being said, I have no experience dealing with this type of fraud, or any for that matter. Any advice would be of great assistance. There is much more shady stuff being done by a particular broker here in SD on this house and I'm sure on others. 

Can anyone chime in on what they would do or have done is such cases?