Well, you could drug test anyone who was there, and it isnt 100 different people. All staff are already drug tested, so that narrows the search down dramatically.Depends where the found it. If it was out in the open it would be easy. If it were hidden somewhere in a bathroom without cameras that may have been frequented by 100 different people over the last month, it might be near impossible to know who. The clue might be the person with the white powdered nose who left the bathroom though.