It depends on where you work.... In Las Vegas, the Investigator is the one who goes to the scene and collects the evidence. The Technician is the 'scientist' back at the lab that is going to analyze the evidence. I hope that helps.
Maybe some people take charge of both responsibilities.
and I have an assumption on robberies. Criminals rob Jewelry shop and steal a lot of Jewelry which is made of metal stuff.
Then Crime Scene Technician or Investigator can use technical equipment to investigate and search for the proofs to arrest criminals.
Under different circumstances, police can use super scanner metal detector to find where criminals are.
Here in Florida a lot of us are not sworn (civilian employees) who do not have arrest powers and are commonly referred to as Crime Scene Technicians. For those agencies where their Crime Scene personnel are sworn / arrest powers / carry a gun etc. they are called Crime Scene Investigators. Though not always the normal and it varies from agency to agency.