Children write messages for the passengers of MH370 on a wall in Kuala Lumpur airport - Reuters

Investigators looking into the disappearance of Malaysia Airlines flight MH370 have discovered a “mysterious 200lb load” added to the flight list after take-off, according to an engineer whose wife and two children were on board.

Ghyslain Wattrelos said the cargo was revealed in a report on the passengers and baggage by French investigators.

Mr Wattrelos, who believes the flight was deliberately downed, told Le Parisien newspaper: “It was also learned that a mysterious load of 89 kilos was added to the flight list after take-off. A container was also overloaded, without anyone knowing why. It may be incompetence or manipulation. Everything is possible. This will be part of the questions for the Malaysians.”

MH370 became one of the world’s greatest aviation mysteries when it vanished with 239 people on board en route from Kuala Lumpur to Beijing on March 8, 2014.

French investigators who examined flight data at Boeing’s headquarters in Seattle believe that the pilot was in control of the airliner “right up to the end”.

Mr Wattrelos said the investigators told him the data “lends weight” to the theory that the pilot crashed into the sea in a murder-suicide, although they stressed that there was no proof. The investigators expect it to take up to a year to examine the data fully.

However, some experts believe a hijack by a stowaway is a possibility and the mysterious load could lend credence to the theory. Tim Termini, an aviation security specialist, told Channel 5 earlier this month: “It’s highly likely that a hijack took place and again, there’s four options for the hijack.

"One is the hijack of the aircraft through a crew member. The second is a hijack coming from a passenger. A third option, which is a fairly unusual one, would be a stowaway. And then of course the fourth option is an electrical takeover of the aircraft from a ground-based station.”

Mr Wattrelos, 54, who has led a campaign to find out what happened to the flight, acknowledged that “there is a risk that I may never learn the full truth.”

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