Educational requirements vary from agency to agency. Some require a High School diploma or GED while some require a BS in a hard science.
There are over 200 CSI and Forensic Science jobs listed in the employment opportunity page of the Crime Scene Investigator Network. Look through the job listings to see what the different agencies require in education.
My advice is to decide where you want to work, find out what they require in education, and then get that level of education.