Final answer:
Team killers average 13 to 18 victims per case, with the dynamics of group activity likely contributing to the higher victim count. The correct option is C.
Step-by-step explanation:
In the study concerning team killers, it was found that they average 13 to 18 victims per case. Team killers, also known as serial killers who work in pairs or groups, often have a higher victim count per case compared to solitary serial killers.
This phenomenon can be attributed to the dynamics and logistics of committing the crimes as a team, allowing them to target more victims, evade detection, and sustain their activities over an extended period.