There is a lot of competition for CSI jobs. One thing an employer will look at is your grades. You should have at least respectable grades, like a B average, to be a viable candidate. The employer looks at a lot of other things too, like what classes you have taken (biology and math) and experience (volunteering at a law enforcement agency or some sort of laboratory).
Also, there are over 250 jobs listed in the employment opportunity page of the Crime Scene Investigator Network. Many are entry level jobs. Look through the job announcements to see what employers require. You will find that many jobs require a degree, but some do not. Of course, you will be more completive if you have a degree.