If you get a degree is Biology or Chemistry you do not need any other degrees. It would be unnecessary to get a degree in Criminal Justice.
If your goal is to work as a Forensic Scientist in a Crime Laboratory you will need a BS degree in Biology or Chemistry. If you want to be a Crime Scene Investigator or Evidence Technician you can often qualify with less education. I would suggest you stay clear of just a Criminal Justice degree unless you have a significant portion of your training in Crime Scene Investigations.
For someone who wants to be a CSI, or just has a Criminal Justice degree, I suggest they consider getting specialized training in Crime Scene Investigations. There are programs that focus just on Crime Scene Investigations. One such program is the Crime Scene Investigation Certificate Program offered at the University of California. They have a Summer Academy in which you can receive specialized training in Crime Scene Investigations and receive a certificate upon successful completion of the program. The Summer Academy starts in July each year and runs for five weeks. People come from all over the United States for the five week training. A certificate for more specialized training will make you more marketable. Here is the link for a brochure on the program: CSI Academy brochure. To enroll or receive more information: Crime Scene Investigation Summer Certificate Program.
I happen to teach in the CSI Certificate program and can tell you we have had several students go on to get jobs as Crime Scene Investigators.
My advice is to decide where you want to work, find out what they require in education, and then get that level of education.
There are over 600 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.
I am in the state of Rhode Island and I am having a very difficult time finding a school who offers crime scene investigation. Would you be able to offer any guidance for me? I am 45 minutes away from Massachusetts and I don't mind commuting. I found Kaplan University but it's only online. I am looking for hands on. Thank you in advance. If you can forward a copy of your response to my email I would greatly appreciate it.