Cordoning off a crime scene for collection of forensic evidence, and analysis of the collected evidence, could be conducted by any number of NGO job descriptions. Legal standards for chain-of-custody can exist in a market-based system the same way other technical standards exist in any number of industries.
Just curious. Absent a police force paid by taxes, how are the free market investigators paid?
Most crimes are committed against poor people, who don’t have the money to pay for an investigation.