The door of the neighbor’s house was wide open, rocking slightly with the breeze, when Tammy Hansen returned to her midtown Gainesville home with her teenage daughter and toddler son one day this past week. But the neighbors had vacated months before, and Hansen began to worry that squatters might have found a place to hole up as the night air chills and winter approaches. She called police officers to inspect the place, and they found no one inside.