How did the identification of one body (Sergio) lead to the identification of five additional victims?

The correct answer is:

Five additional victims were identified with the identification of Sergio's body because in the same grave were five other victims who was executed the same day as Sergio, on March 29 of 1984.

Pecarreli's team went to Guatemala to look for the bodies of victims of the Civil War in Guatemala. He also wanted to give closure to the families.