Among the mysteries about the crash of Swissair Flight 111 off the coast of Nova Scotia in 1998 is what happened to diamonds, rubies, emeralds and other gems that were supposed to be in the cargo hold.

Today they would be worth half a billion dollars.

Very little is publicly known about the gems. Three days before the crash, a popular exhibition, The Nature of Diamonds, closed at the American Museum of Natural History in New York. At least one piece from the exhibit was being shipped aboard the Swissair flight on Sept. 2.

Whoever had lent the item to the museum did not want any other information disclosed.

A total of one kilogram of diamonds and 4.8 kilograms of jewelry was being shipped on the plane. Jewelers regularly used the airline to transport gems.

The flight took off from JFK airport and then began to fly over the Atlantic Ocean, destined for Geneva, Switzerland, but a little less than an hour into the flight the crew noticed smoke and issued the international urgency signal "pan pan pan."

They were cleared to proceed to the airport in Halifax but crashed in the relatively shallow water off Peggys Cove, N.S. All 229 people aboard were killed.

98 per cent of plane recovered

The recovery effort, Operation Persistence, retrieved 98 per cent of the aircraft and much of the 16 tons of cargo. That effort included use of a suction-dredge vessel, which also retrieved rocks and other objects that had been at ocean bottom.

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Investigators catalogue debris from Swissair Flight 111 in Halifax on Sept. 10, 1998. By the time the investigation concluded, no sign of a valuable shipment of diamonds had been found. (Reuters)

After being brought to the surface, the pieces, which numbered about one million, went to a sorting facility in Sheet Harbour, N.S. None of the diamonds and gems, or the stainless steel tube that held them, were found.

Other valuables were also in the cargo hold: a consignment of watches weighing two kilograms, almost 50 kg of paper currency from a U.S. bank and a painting by Pablo Picasso, Le Peintre (Picasso did several paintings with that title.).

Some of the watches, some currency and 20 square centimetres of the Picasso painting were recovered. Normal practice was to place all valuables in the same cargo hold container.

During the recovery effort, Swissair said in a statement, "It should be assumed that the valuables container did not remain undamaged in the crash."

What could have happened to the jewels? Had they really been onboard? Had unscrupulous divers taken them? Had they disappeared into the ocean?

Given the security for the recovery effort, it seems unlikely the diamonds could have been stolen during that time. It is also hard to understand how the shipping tube, or the jewels if it the container had disintegrated, could have had enough velocity to significantly penetrate the ocean floor.

Lloyd's plans to search for diamonds

Insurer Lloyd's of London paid out an estimated $300 million for the diamonds and jewels — their value at the time.

Watch The Fifth Estate documentary

The Fifth Estate investigates the crash of Swissair Flight 111 and reveals more on the stunning allegations on Friday, Sept. 16, at 9 p.m. on CBC-TV (9:30 p.m. NT). The documentary will be rebroadcast on CBC-TV on Sunday at 11 p.m. (11:30 p.m. NT) and on CBC News Network on Sunday at 7 p.m. ET and Tuesday at 10 p.m. ET/PT.

The documentary is also available online via the video link in the right column, above.

In 2000, CBC broke the story that Lloyd's had applied to the Nova Scotia government for a treasure trove licence so it could search the ocean floor in what was then a restricted area. Their plan was to use a small submarine to vacuum the ocean floor, something the investigators had already done. Some considered it a sacred area.

Lloyd's plans outraged many of the victims' relatives. "People were out there in a sea of blood," Ian Shaw told CBC reporter Rob Gordon. Shaw's daughter Stephanie had been onboard.

The anger did not dissipate and a few days later, the company informed the government it was withdrawing its application.

"Lloyd's would like to apologize to all families of the victims of the Swissair crash for any distress caused by its application for a licence to a right of recovery in the crash site. Lloyd's will not dive or explore the site," a company news release said.

Accident investigation but no criminal investigation

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As part of the crash investigation, 98 per cent of Swissair's aircraft was recovered, and much of the cargo. The plane crashed Sept. 2, 1998. (CBC)

RCMP crime scene investigator Tom Juby, who was assigned to the Swissair Flight 111 investigation team, told the CBC's The Fifth Estate that he thought there should have been a full-scale criminal investigation into the crash, because of his doubts about the cause of the onboard fire.

Had that happened, there would have been more certainty about whether or not the diamonds and jewels actually were in the cargo hold. However, the Transportation Safety Board conducted an accident investigation, with the RCMP providing assistance evaluating the crash evidence.

The RCMP did not conduct a criminal investigation. Thirteen years later, the fate of a stainless steel tube and its valuable contents remains unknown.