She then kept hanging around the building so I called the police.  

The thing is, sometimes the tenants don't get along but I encourage them to call the police on each other.

In other words, could that property be sold before the probate case is closed, if the descendant (that inherited the property via the will) chose to do so?

The neighbors said he never answers the door, not even for the police (apparently he was suspected of stealing neighbor's yard sale signs).

He only went off the police report that I filed before a contractor got involved with the clean up and discovering the extent of the damage.  

The police were unable to serve her and now I have to hire a special process server. 

I understand you don't think its serious, but after seeing vandalized homes, I can assure you if you are found in a property you do not own, or with a licensed agent, you could face trouble with the police.

How long will it be before we see a situation where either the police and/or the foreclosee get killed in one of these situations?

When she discovered this, she called the police.

Policing the tenants really comes down to a management responsibility.