Poltergeist Activity

A friend recently related a story to me about the place where he works. He said that some strange things have been occurring there. Voices can be heard after hours in an otherwise empty building. Items will go missing only to be found later in the most unlikely places. One morning he said that upon arriving to work early he had found numerous items scattered about the work area. Upon asking fellow employees if they had moved the items before they had left the night before, the response was "No".  The longer fellow employees work at this place, the more their personality seems to change. And not in a good way. 

Is this the result of poltergeist activity?