There are a few avenues you can take. You can apply at local Sheriff's Departments, Police stations and the like and start in other areas within the department. Some offices will hire without formal education but lean heavily on prior experience. You can start volunteering and putting yourself out there and gain entry to the crime scene investigation department that way.
You can also approach it academically and earn a degree from an accredited program. This can be done remotely and in person depending on your program. These often require an internship which is a great way to get your foot in the door at an agency. It will give you free real world experience and in the end make you more appealing to future employers.
I've seen both paths and know both types. One that has started from "the ground up" without a formal education of any kind and one that is entering the field with a masters degree. I will say the field is highly competitive so any way that you can make yourself stand out do it! That means certifications (are offered as part of degree programs sometimes and can be obtained without a degree) volunteering experience etc
To be CSI, four steps are involved:
Step1: Earn a Bachelor’s Degree in a Related Field: recommend major: Criminal Justice, computer science, forensic science, or Biology
Step3: Earn CSI certifications and State Licensure
Step4: Higher education could provide advancement opportunities
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