In this country a cause of death will not be stated on a death certificate unless an autopsy is done. Muslims prefer their departed to be buried quickly. Hint for foreigners who don't understand: They died from a plane crash.
It might be useful to rule out signs of burning / explosion / bomb? If there is evidence of drowning, that would suggest the aircraft impacted the water gently enough to keep passengers unconscious but alive. The bodies may hold clues that the plane broke up at altitude, which has implications in the search for the fuselage.
These are unpleasant thoughts, but I'm surprised the bodies have been returned to relatives so promptly. Not all the passengers were Muslim.