Six altogether four for BS and two criminal justice degree
you must serve 8 years before you can becomee a crime scene investigator
The above answer is some what silly, as it does not provide a correct reply to the question.
A Police officer may attend a special course to learn the BASICS of crime scene work. BUT a college course of at lesat two years would be much better preperation, and would get you a position sooner than a basic course at some state Police academy that lasted a few weeks.
Forensic science is exacting and precise. If you are not that kind of person, take a pass.