ballistic identification: identification of the gun that fired a bullet from an analysis of the unique marks that every gun makes on the bullet it fires and on the shell ejected from it
identification: evidence of identity; something that identifies a person or thing
circuit: (law) a judicial division of a state or the United States (so-called because originally judges traveled and held court in different locations); one of the twelve groups of states in the United States that is covered by a particular circuit court of appeals