The social anthropologist conducts two types of interviews: an antemortem interview and a historical interview.
The antemortem interview ("pre-death") helps to establish a skeletal medical record. It's a sort of history -- an osteological history of the skeleton. Investigators ask family members questions like, "How old was he? How tall? Did he work with his left hand or with his right hand? Did he ever break a leg? Did he ever complain of tooth pain? Did he have all his teeth? Was he born OK? Was one of his arms shorter? Did he walk funny? Did he ever suffer any illness?" The answers to these questions are reported to the physical anthropologist who refers to them in his analysis of the skeletal remains.
The historical interview tries to piece together what happened. Witnesses and survivors are asked questions like, "What happened during the killings? What happened to the survivors after? What happened to the bodies? Where were they buried?" Investigators use this information to pinpoint the location of the graves. It is often the case that family members and neighbors buried the victims. If the trauma they describe in their interviews is found on the skeletal remains, it gives credibility to their accounts and strengthens the case against the perpetrators.
These historical interviews happen before, during and after the exhumation. In fact, it is often during the exhumation that additional witnesses come forward with their testimony. The fact that actual work is being done to unearth past crimes seems to give people the courage to speak out about what they saw. In this sense, collecting witness accounts and the process of exhumation go hand in hand.