That's really amazing. But, just being the Devil's advocate here, the situation is this.
Law enforcement can't do anything because they don't know the whole story. And people living in a house, with utilities in their name...have rights. OK, so the home owner says "I just bought this house, these people don't have any lease or rental agreement." And law enforcement says, "Did they have one with the last property owner?" Don't know. Have to be handled via eviction.
And, face it, people lie. The squatters say "Yes, we have an agreement, but we didn't write anything down, all done verbally and a handshake."
As long as they are in the house, they have rights. And to make it even worse, now you can't collect rent from them while they are there, because that would give them even more right to stay and you couldn't get them out without an eviction. And if they are smart enough, they can protest the eviction and delay it for months.
Be best to just annoy the crap out of them and make them leave. Stink bombs under the house, as the landlord you can make inspections of the property at will...do a lot of them, at meal times, during the "movie hour", Saturday morning at 6AM... you get the idea. Shut the water off (everybody has a T-handle right?), go by at 2AM on a week night and shut the main breaker off (no alarm clocks, fridge and freezer off for hours, no so much hot water in the morning). Lots of stuff you can do to make their life less happy.