In primary schools -and in some cases, higher-level institutions too- we usually have the mystery of finding who actually made that pungent scent that pricked our olfactory senses....simply due to the fact that 85% of the time, the guilty is too embarrassed to own up to his mistakes.
In my opinion, it is simple, really.
The guilty is usually the one who (loudly and quickly) points finger to the nearest person to him/her as to immediately make an accusation that is obvious to everybody.
Then, having smelt that the "source" of the fart had come from around the accused's vicinity, people surrounding the accused would immediately back the guilty's charges...leaving the accused alone and vulnerable to public shame in his/her defences.
I knew about all this because I used to be the accused. And I hated being one, because I already know who the guilty was, yet I could not point my finger back at him/her on the basis that he/she has pointed his/her finger on me first.