Bicycle detail

My bike was parked under the stairs in our 4-unit apartment building, as usual, and like the other 3 bikes under there. I went down to grab it and to ride it this morning, and it was gone. Last I had seen my bike was Sunday afternoon. I asked the neighbors, and nobody has taken it or seen anyone take it. There are only the following persons who have a key to enter our building: the occupants of the units, the landlord, the mail man, Sunset Scavenger. Sunset comes in every Monday morning through the garage area, which is open to the stairs. All I can guess about what happened is that someone either snuck into the building during trash collection, or someone from Sunset decided to help themselves, or a visitor for one of the neighbors decided to help themselves with my bike sometime between Sunday night and this morning. My bike was the nicest looking one, and the one in front of the other bikes, so it was the easiest to grab. We have been storing bikes at this location for the last 5-6 years, and this is the first time one was stolen.