He is technically now your tenant. Our purchase contracts protect the buyer by making arrangements for the seller to pay rent to the buyer if he does not vacate by the agreed upon date. Without a contract, spelling out his duties, you may be left to the local authorities. Also, if he is "tearing up the house" the damage would fall under your insurance.
Sounds like you might be an investor, or at least buying from someone who's in distress? (You said, "He has already been paid to move.") If you have a Realtor, get his/her advice. If you're a real estate investor with a mentor, check with the mentor. The cheapest option would be to pay him a bit more to move, but this time you make sure it happens. You arrange it with him, pay for the movers, and throw in a bit of cash. You pay him only when he's out.
Sounds as if he may be on drugs--out of money, no place to go, house in shambles. Just a little bit of money (enough for his next fix) probably would do the job. Or: Check with a lawyer before doing the following. But, if he's using, call the cops on the drug problem. As soon as he's hauled off, you go in, move all of his belongings into storage, and change the locks.
But my first option would be to offer him enough for his next fix, payable once he's out.
There is not much you can do about him if you do not own it yet so try to reason with him.
Have you asked your atty or agent yet as to what your state allows?