Ghosts in the Office

I work in a historical building.  It's long been rumored that it's haunted.  For years, I've been blaming misplaced files on Mortimor the Ghost. About 15 years ago I was getting new carpeting in the office and the carpet layer looked at me strangely and said, "Who is that man standing in back of you?"

Huh?  There was not anybody in my office.  I shrugged it off.

My building is really creepy sometimes.  I could go on and on about weird instances over the years, but I will refrain.  The past year or so I've been visited more and more frequently by a male, shadowy figure that walks past my office door.  Even my assistant notices and has said something -- and she is NOT somebody who believes. 

This shadowy figure is now getting noisy.  Yesterday shortly after 5:00 a loud, forceful knock was at my door and the mail slot opened, but nothing came through.  I thought perhaps it was an UPS delivery or something of the like so I jumped up to catch the delivery person before s/he left.  My office is at the end of a hallway.  There is NO way s/he could have left that quickly.  There was nobody there.  I even jogged down the hallway hoping to catch whom I thought the delivery person to no avail.  I even called out loud. 

No mail note, no UPS note, no FedEX note.  Nothing.