The police will not remove squatters, they will tell you it's a civil matter. You'll just have to evict "Any Unknown Tenants in Possession". If they are moved in with their belongings in the house the police will tell you that they're living there and there's nothing they can do. If they have utilities on or receive mail at the address it's a rock solid case for them to show they are "tenants" even if they don't pay rent or have a lease.
This has happened to me a couple times, once a tenant died and some homeless people ended up with her keys. They moved in and we didn't know for a week and by that time they were able to establish that they were living there and the police wouldn't help me so I had to evict them.
The second time we had a vacant rental and sometime in a 12 hour window between showings someone broke in through a window and moved a whole bunch of crap in there. We called the police and reported the burglary and since no one was there, no furniture was in the home and no utilities were on there was no reason to think that anyone was actually living there. The police told us to put any of the belongings inside out on the curb and secure the house. The neighborhood vultures grabbed all of the belongings up in about 5 min, arguing over who got what (class D area).
About 8 hours later we got a call from a neighbor that the same people were back trying to get back int he house so again we called the police. Their story was they found the house on craigslist (at a price of about half what we were asking and all utilities included) and sent $1,100 via MoneyGram. The police told them to move along and not to come back on that property. I'm not sure if their story was true or not but if it was they are idiots for thinking they could rent a house without ever seeing the inside first, not filling out an application, not getting a lease, not getting keys and the house not having utilities on with"all utilities included." The police told me if they were there with their story about renting it and their belongings were still in the house I'd be stuck evicting them, even though they had broken in through a window in between showings.
In the 2nd case I think that was borderline and would depend on the officer or department policy. If they have utilities on and get mail there forget about getting any help from the police, you have to evict them.