CID Dhoom – Under Water Action

A group of boys gone for scuba diving, find a dead body of a scuba diver. CID investigates and traces his identity by the serial number on the oxygen cylinder. The deceased was a famous scuba trainer, Dharam, and his death showed lack of oxygen as the reason but the cylinder was almost full so it was a case of murder. The weeds on his cloths indicate that he has been death for some time. What could be the mystery behind this mysterious death?