Being a medical examiner requires more schooling than many other careers in criminal science. A student wanting to be a medical examiner--someone who performs autopsies to determine the manor of death--needs to complete an undergraduate degree, usually in a science field, and a medical degree. After medical school, a student must do a residency in forensic pathology. The undergraduate and medical school degrees take about eight years. The residency adds additional time.
Crime scene technicians need only to have graduated high school or have an equivalent degree, such as a GED. Some jobs require that crime scene examiners be police officers, though many do not. Crime scene technicians gather evidence at the crime scene to be analyzed later, so they work with police officers, even if they are not officers themselves. Beyond a high school degree, a certification in crime scene investigation may be required. You can obtain a certification from an online or traditional school depending on how much time you have and when you are available. A crime scene certification typically takes one year.
Crime laboratory analysts need a four-year college degree in a related science field, such as chemistry or biology. They perform tests and analyses on evidence gathered at the crime scene. The lab work is science intensive for this career, so the schooling required is more than you would need to be a crime scene technician but less than you would need to be a medical examiner.
If you are interested in the psychology of crime and in creating a psychological profile of a criminal based on evidence and the nature of the crime, then you need both an undergraduate degree in a field that will support further study in psychology and a graduate degree in psychology. A traditional undergraduate degree takes about four years, and a doctorate usually take another five years.