Three of the four people who were on board a plane that crashed in New Caledonia last weekend had been drinking, including the pilot.
The territory's deputy prosecutor said initial tests had shown traces of alcohol in the victims.
The four-seater plane crashed in the early hours of Saturday, instantly killing three of Lifou's air traffic controllers and a French tourist.
Investigators have so far found no explanation for the crash, and an examination of the wreckage is expected to be carried out in France.
The crash has shocked the community on Lifou, and psychological support is being offered.
The local congress on Wednesday observed a minute's silence.