Final answer:
An investigator must keep the client informed and provide a report of investigation.
Step-by-step explanation:
The requirement for an investigator regarding keeping the client informed and providing a report of investigation is option 4) An investigator must keep the client informed and provide a report of investigation. This means that an investigator has a responsibility to regularly update the client on the status of the matter they are investigating and also provide a written report detailing the investigation's findings.