Ditto what Bryan (Ia) said. Also removing non-evicted tenant's property from the premises is illegal too. I believe it is called "stealing" I am surprise they haven't called the law on you. You may luck out and they don't really know their rights as a tenant, therefore they don't realize you can't lock them out without the Sheriff (in my state, Marshall or Constable in others) standing right there.
They actually did call the law. The day I changed the locks they came by and couldn't get in so they called the sheriff. The sheriff told them to call me because it was a civil matter, not criminal, therefore he refused to get involved.