The pilot of Malaysia Airlines flight MH370 was in control of the plane “until the end”, French investigators reportedly suspect, after gaining access to "crucial" flight data.

The readouts "lend weight" to suspicions that he crashed into the sea in a murder-suicide, they were cited as saying.

The revelations based on Boeing data came days after a new account suggesting the pilot may have been clinically depressed, leading him to starve the passengers of oxygen and then crash the Boeing 777 into the sea.

MH370 was on its way from Kuala Lumpur to Beijing on March 8, 2014, with 239 people on board, when it vanished and became one of the world's greatest aviation mysteries.

In July last year investigators released a 495-page report, saying the plane's controls were probably deliberately manipulated to take it off course but they were not able to determine who was responsible.

The only country still conducting a judicial inquiry into the crash is France, where two investigating magistrates are looking into the deaths of three French passengers, the wife and two children of Ghyslain Wattrelos - an engineer who met the judges on Wednesday.

According to Le Parisien, they informed him that Boeing had finally granted them access late May to vital flight data at the plane maker’s headquarters in Seattle.