I work in the outbound at my center and the other night our work area misloaded a bag. Our PT Sup does not choose to redistribute the loads during wrap-up so we have two people covering the belt and its almost impossible to say who loads what at the end of the night. Management has decided that since they can't be sure who is responsible for said bag that both people who were in the area are going to receive warning letters. My question is in regards to the grievances my coworker and I will be filing. What should be the focus? Would be better to say the it falls on the supervisor for not assigning people to certain trucks, losing accountability? Absence of evidence? Is there any precedent to a case like this? Any insight is great appreciated, thank you.