Forensic Science is the best major to choose if you wish to become a CSI. You can get an Associates degree (2-year) or Bachelors degree (4-year). Keep in mind that many police departments will require a Bachelors degree. However, you could also study Criminal Justice or Criminology, but you will still want to have a focus on Forensics. If you have a Bachelors degree, go after a Masters degree, which will greatly improve your value when you are applying for the job. In general, you will also earn a higher salary with a Masters degree.