Who are they and what do they do? The criminal investigator provides expertise in criminal legal investigations.
What are the activities of the job? Research at the crime scene (to collect evidence), enquiring into the circumstances of violent death due to unnatural causes, reconstructing the crime situation, making decisions about a person's guilt or partial involvement in a crime, collaboration with the forensic expert, writing reports and interpretations on the evidence.
Where is it done and under what conditions? At the office and at the crime scene.
What tools/equipment do they use? Microscope, reflecting powder, brush, car, computer, copy machine.
What do you need to succeed? You need higher education (e.g. BA degree in law); capacity to respond to emergency calls, patience, intuition, empathy, ability to work in a team of experts. In some countries this role may be carried out by police officers or detectives who are still part of the police force and designated to work as a squad on particular types of investigation. A background in more general police work will then be necessary before being promoted to this sort of role.