Mystery has surrounded MH370 since it's disappearance. Here's a look at the theories suggested over the years.

Investigators looking into the disappearance of flight MH370 say they have discovered a 90kg load that was only added to the cargo list after takeoff.

French engineer Ghyslain Wattrelos, who lost his wife and two of his three children in the crash, submitted a new report detailing the claims to investigative judges in Paris last week.

He says a container on the flight was also found to be overloaded, but no explanation was ever established.

Four French citizens were lost on MH370, and France is the only country with an investigation into the incident still ongoing.

“It was … learned that a mysterious load of 89kg had been added to the flight list after takeoff,” Mr Wattrelos told Le Parisian.

“A container was also overloaded, without anyone knowing why.

“The expert draws no conclusion.

“It may be incompetence or manipulation. Everything is possible.

“This will be part of the questions for Malaysians.”

Mr Wattrelos also said different versions of the flight’s passenger list contradicted each other.

Theories about the crash have also focused on a shipment of lithium batteries that were on-board the plane.

Two months after the incident, NNR Global revealed it had shipped 2453kg of items on the plane, of which 221kg were lithium batteries.

It had been suggested the batteries could have sparked a fire, but the idea was called “highly improbable” by the Malaysian Government’s final report on its own investigation into the crash.

In another twist in to the aviation mystery, French investigators have reportedly said the pilot of missing Malaysia Airlines flight MH370 — Captain Zaharie Ahmad Shah — is thought to have been in control of the plane “until the end”.

A team of investigators given access to Boeing flight data at the company’s headquarters in Seattle told French media about the obvious abnormalities during the flight.

“Some abnormal turns made by the 777 can only be done manually,” Le Parisian quoted an investigator, who was not named because they had signed a confidentiality agreement with Boeing, as saying.

“Someone was at the helm.”

AVIATION MYSTERY

Flight 370 disappeared on March 8, 2014 en route from Kuala Lumpur, Malaysia, to Beijing with 239 people on-board.

Just 38 minutes into the flight it lost contact with Malaysia Airlines.

The disappearance has been dubbed one of the greatest mysteries in aviation history.

The search for the missing plane, which became the most costly ever conducted, initially focused on the South China and Andaman seas.

Data from the aircraft’s automated communications later identified a possible crash site somewhere in the southern Indian Ocean, but no wreckage could be found.

Malaysian and international investigators believe the jet veered thousands of kilometres off course from its scheduled route before eventually plunging into the Indian Ocean.

Estimates for the plane’s likely location could be made using data showing its distance from a fixed satellite but required knowledge of how fast the plane was going and in which direction before the crash.

If it was flying north, possible locations could stretch as far as the border between Kazakhstan and Turkmenistan to Thailand.

But if it was flying south, possible sites could range from Indonesia to the southern Indian Ocean.

So far debris believed to be from the plane has been found on beaches in Malaysia, Mozambique, and Tanzania, and authorities now believe the plane is most likely to have gone down in the Indian Ocean.

More than 30 bits of aircraft debris have been collected from various places around the world, but only three wing fragments that washed up along the Indian Ocean coast have been confirmed to be from MH370.

THE MAIN THEORIES OF MH370 DISAPPEARANCE

Pilot or co-pilot suicide: Captain Zaharie Ahmad Shah may have intentionally downed the plan in an act of murder-suicide. The report shows the aircraft was deliberately turned off course, but investigators say they found nothing irregular with Mr Shah’s background, training and mental health. MH370 may have also been downed by the co-pilot. Fariq Abdul Hamid was on his first flight on a 777 as a fully approved first officer.

Hijacking: Chief investigators says they cannot rule out a “third party” hijacking the plane. However, no terror group has claimed responsibility for the crash, and there is no evidence the aircraft was being controlled “remotely”. Also, the report shows none of the passengers had experience of flying a plane

Fire or fumes: One theory is transporting lithium-ion batteries could have caused a fire. These batteries, which are used in mobile phones and laptops, may have exploded or been set alight. A haul of tropical fruit that was off-season could have reacted with the batteries — causing them to ignite or create hazardous fumes

Hypoxia: Passengers and crew could have been incapacitated by an unknown hypoxia event — a deficiency of oxygen in the cabin. This theory claims Mr Shah would have been unconscious for hours.

This article originally appeared on The Sun and was reproduced with permission