let truth be on my lips

We have a reward system. Students get "money" for good behavior or behavior out of the ordinary. It allows them them priviledges. This 2 weeks it was playing basketball as teams, enough points and you can be a captain. We noticed one problem student with a huge wad of it. The teachers got together at a meeting and started asking who was giving him money. None of us had been or not that much. To qualify the money needs the student's name, our signatures and dates. Finally the administrator took a look at them, walking him around the school asking each teacher to verify the signatures. Sure enough he had forged them. That doesn't bother me, not really. What does is he is keeping to his story that he put his money down on a table and somebody must have put all those forged "bills" into the stack.