Final answer:
The wounds on the decedent's abdomen are considered to be exit wounds, appearing irregular due to the concrete surface against which the decedent was lying when shot.
Step-by-step explanation:
Matthew, the death scene investigator, believes that the wounds on the decedent's abdomen are B. Exit wounds. This assessment is likely based on the fact that the decedent was lying prone on a concrete surface when shot, which could cause the exit wounds to have highly irregular abrasions due to contact with the hard surface. The high velocity of the bullet leaving the body would cause the skin to stretch and abrade against the rough concrete surface, potentially resulting in the irregular appearance of the exit wounds, despite the detective's initial doubts.