Removing squatters from house in Oregon

[Scott Kirk]

I'm in communication with a property owner in Oregon who is trying to remove some squatters from their property and they don't know how to do so. 

The back story: The property owner allowed his mother to stay at one of his residences and she invited someone to live with her.  At some point she moved out and the lady who had permission invited a large number of people to live with her.  These people are criminals and likely have warrants out for their arrest.  The lady who had permission was arrested and is currently in jail for a few years.  Everyone who is currently residing is doing so without permission from the owner.  They likely have hard drugs like meth on the property as well.  Is this something that we can simply call the police to get them out?  Or are there private companies we can hire to forcibly remove them?  Your help would be very much appreciated!