Can't Find the Smoking Gun

We have had a serious problem lately with someone smoking in the library.  Whoever it is, we cannot catch them on our security cameras.  They are going up beyond the second floor to the third landing at the roof access door.  When we enter the stair well later, the smell of smoke is obvious.  Before people start thinking I am just over sensitive, several staff people have brought this to my attention (since I monitor the security cameras in the library) and I am a smoker myself, so it's not just that I am anit-smoking.  I really enjoy smoking, I will be honest.  However, I know to out outside to do so.  Is it hot as hell outside? Yes.  Is it inconvenient? You betcha.  Would I rather sit in my office and have a smoke? Sure.  But too bad.  I suck it up and go outside in the heat if I want to smoke.  And I don't stand by an entrance either, so that people have to walk through my cloud of smoke to get in the building.  I try to be a considerate smoker.  I don't litter my butts on the ground, I don't block entrances/exits, and I try to stay downwind if I am walking with a non-smoker.  It's called basic courtesy.  But not only is smoking in the library discourteous and a fire hazard, it is against Library, University, and State of NC rules and regulations.  There are legal repercussions to getting caught.  Smoking inside a state building where no smoking is allowed, is a stupid thing.  Why risk legal trouble for a cigarette you can enjoy just but going a little bit further out of the door?  We have a few suspects in mind that we are keeping an eye on, and we are increasing our in person monitoring of the stairwells with more frequent rounds.  I want to catch this person so badly.  And when I do, after I turn them over to campus police, I will go outside and enjoy a smoke in my car and relish my victory.