A 4n6nurse gave you an excellent reply. What I would add to it is that rather than trying to make what you do for a career fit your education, why don't you sit down with a career counselor at the college and find out what exactly it is that you want to do. Then get the eduation and credentials to do that.
I started out as a double major in forensic science and chemistry. In the easiest semester there was, I had General Physics, General Chemistry, Calculus I, and English Literature. In real forensic science, you become a scientist where you work in a lab running tests - it's not crime scene work, you don't work for the Medical Examiner or with death investigators, and it's not nursing. Although I did well grade-wise, I learned that I was not a lab person. After talking with a number of people and researching what I wanted to do (saw the gap between medical and legal and learned that I wanted to bridge the gap in clinical forensic nursing in the ED), I spent seven years (part-time) earning a degree in Criminal Justice - Investigative Services. During that same time period I also went all the way through nursing school, and spent two years just learning how to be a nurse before trying to specialize. Today I am one year short (out of three) of my MSN as a Clinicial Forensic Nurse Specialist, I work as a nurse in an ED and yes, I do a clinical forensic nursing role within my ED role. It's taken me years to get to this point, but I am doing it. And I had a plan.
Just so you know, collecting physical evidence at crime scenes is the role of law enforcement, not of forensic scientists, or nursing. Processing the body at death scenes is the role of the Medical Examiner's (ME's) office - the death investigators are the eyes and ears of the ME at the death scene. The roles of the Forensic nurse are many and varied, and include SANE and being a death investigator (doing one role doesn't necesarily you also do the other, I recently did the coursework and clinical time to become a SANE in the ED). Death Investigation is very popular - and extremely competitive right now - as everyone has been bitten by the CSI bug and wants to do that role. Two-thirds of my MSN class wants to do that role. Right now, the supply outweighs the demand in that job market (due to the CSI effect).
As a4n6nurse pointed out - you have to have a license to do any kind of nursing. I am not sure why a Forensic Nursing certificate would be awarded to someone not in nursing, but you can get into trouble if you give the impression of being a nurse when you are not.
Bottom line - know what you want and get a plan before you spend thousands of dollars and hundreds of hours studying something you might not want to do if you knew what it really was. Hope this helps. 4n608