When One Refers to the "Layer Checking Technique" in Arson

When one refers to the "layer checking technique" in arson investigation,what is being described is the

A) process of checking through the layers of material stacked on top of each other after a fire.
B) analysis of materials for the presence of accelerant.
C) investigation of all suspects beginning with the prime suspect and working down to the least likely suspect.
D) method used to identify the most likely motive.