I imagine it wouldn't be easy not even for local tax advisor to explain this because tax officers or in worst case financial police could quickly come to my door asking me why did i announce the income ( * ) and pay taxes from low amount if incoming bank wire transfer transaction on my bank account shows much much much bigger amount (total selling amount and not the difference amount).

For one, this isn't a criminal matter and so the police will not get involved. 

Best way is to inform your local police.

I contacted a police officer I happened to know, and he came to a meeting of our Neighborhood Watch group held at my house, and consequently saw the activity for himself.

If they are call the police.

It was only a block or two away from a police station and was a 5.7% cap which had me cash flowing right away.

However, he's kept himself out of trouble, for the most part, for the last 7+ years and is the only stable parent to his son, who he has with a woman he's no longer with but often interjects drama into his life still (police calls, charges that get quickly dropped, etc).

That being said, HUD has a "Good neighbor Next Door" Program where they allow Teachers/Police/Fire/EMS to purchase at a discounted rate (50% of asking) as long as they live there for a couple years.

I am also a police officer and see first hand what tenants can do to these properties.

If its not the tenants and no one else has ever come looking for it , I would say its yours  You don't think he should take it to his local police station then.