Egypt-Air’s accident was caused by a fire started by an oxygen mask.

According to the results of French scientists seen by AFP on Thursday, a 2016 Egypt-Air accident in the Mediterranean that killed 66 people was most likely caused by a heart that started from a leaky oxygen mask within the cockpit.

The flight crew evacuated the hearth and appeared to be unable to locate a fire extinguisher, which resulted to the fatal accident a few minutes later.

The five experts said in their 134-page study, delivered to the Paris court of appeal in March and published Wednesday by Italian newspaper Corriere della Sera, that “oxygen seeping through the co-emergency pilot’s oxygen mask is seen as the crucial ingredient in starting the fire.”

Egypt-Air flight MS804 vanished from radar screens on its approach to Cairo from Paris on May 19, 2016. Every single person on board perished.

Initially, Egypt’s aviation minister claimed that a terrorist attack, not a lack of maintenance, was more likely to have brought the plane down.

However, minutes before losing communication, the aircraft sent automated alerts suggesting smoke in the cabin and a failure in the flight control unit, according to France’s aviation safety office.

The latest research does not say for sure what caused the leaked oxygen to ignite.

In June of last year, an expert assessment indicated three possible causes for the fire: “a blanket charged with static electricity that had been asked by the pilot” to sleep, “fatty ingredients in the meal,” and “a blanket charged with static electricity that had been requested by the pilot” to sleep.

The crew was smoking in the cockpit on a regular basis, according to the study, which also noted a pattern of “unprofessional conduct” such as listening to music, frequent comings and goings in the cockpit, and “lack of attention to the flight’s progress.”

The box carrying the co-oxygen pilot’s mask was also replaced three days before the incident, for unclear reasons, according to a June 2018 expert study.

“The repair of this equipment necessitates meticulous verification…, with oxygen leaks being especially harmful,” they had stated.

“There was a failure of maintenance, a string of careless behavior, and major anomalies,” two representatives of the MS804 victims’ families told AFP, urging Egypt-Air to face criminal prosecution.