At least a 4 year degree in forensic science, or criminology, or similar qualifications. The days of cops doing that job are about done, unless you want to work for some really small town department, as the Crime Scene guy.
Any good quality Police service will have more applicants than they need, so be prepared to go a long way, in the USA, to get that first job.
What qualifications are needed to become a criminologist, crime scene investigator, and criminalist?
One option would be a a criminal justice major.
No qualifations are needed
how to become a dinner lady
you require a bachelors degree
you have to be very strong