Tenant refuses to vacate, destroying the house (please help)

[Daniel Pearson]

We're in Utah. This is for a friend. They tried cash for keys, etc. Eviction notice was served, property to be vacated by Oct. 30. There is a strong suspicion of illegal activity. The police have been there several times for domestic violence complaints. The man has been arrested for DUI. But nothing has been tracked back to the actual apartment. They have definitely been breach of contract. 

When is someone considered moved out? When is it legal to change the locks? If they leave and the landlord shows up and sees it vacant, can they assume they've moved out? Extremely frequently, in my experience, problem tenants leave all their junk behind (I've handled this from the flipping side, so never the eviction side). What can my friend do? They're trying to sell the house, it smells strongly of smoke (no smoking allowed). It's just a nightmare situation.

We're just trying to provide as much help as possible.