As I understand it, criminal investigation is an applied science that focuses on solving crimes. Once a suspect is identified, he or she may be prosecuted by a judge and jury under the law.
So we're talking about two distinctly different yet related things here - criminal investigation and law. Is there a term that covers BOTH?
To put it in perspective, imagine suggesting that people study science in order to understand how gravity works, political science to understand how government works and philosophy to attempt to uncover the meaning of life. What would a person study if they want to understand the entire criminal process, from the moment a crime is first investigated to the moment a suspect is sentenced? Is the answer just "study criminal investigation and law"?