Check out the crime scene investigation association its a dot org site it will give you some info and answer some questions.
You can go alot of ways to become a CSI. You can enter through the police field but to get into the field at all you need a Masters of science in a related field like biology or chemistry or forensic science. Try calling your local police station and ask for their recruiter or some one in the csi department that you could ask questions to.
Hope this helps some
Deveri