Toxic gas from human waste killed three sewer workers in the Northern Marianas earlier this month, according to Guam's chief medical examiner.
Aurelio Espinola said hydrogen sulfide inhalation caused the deaths inside a Commonwealth Utilities Corporation sewer well on Saipan on July 7.
Dr Espinola said his findings corroborated initial reports from police investigators that the three were asphyxiated by gas derived from human waste.
The men all worked for USA Fanter Corporation.
RNZ's correspondent in CNMI Mark Rabago said it was alleged the men were not wearing protective gear while working in the well.
He said the Occupational Safety and Health Administration and the utilities corporation had conducted their own investigations, but results were yet to be made public.