An investigator looking into the crash of Swissair Flight 111 near Peggys Cove, N.S., says he was prevented by senior RCMP and aviation safety officials from pursuing his theory that an incendiary device might have been the cause of the fatal fire on board.

"There was sufficient grounds to suspect a criminal device on that plane," retired RCMP sergeant Tom Juby, an arson investigator assigned right away to the Swissair file, told CBC's The Fifth Estate.

"I'm convinced that the investigation was improperly done," he said.

The flight from New York to Geneva crashed into the Atlantic Ocean on Sept. 2, 1998, killing 229 passengers and crew.

The plane carried a Saudi prince, a relative of the former shah of Iran and high-profile UN officials. Diamonds and gems that would be worth half a billion dollars today were also never found.

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Tom Juby, a former RCMP crime scene analyst who spent more than three years as part of the Swissair 111 crash investigation, told CBC's The Fifth Estate, he was 'convinced that there was sufficient grounds to suspect a criminal device on that plane.' ((CBC))

The Transportation Safety Board (TSB) of Canada said that it was an accident caused by a fire in the cockpit. The TSB could not definitively conclude the fire's cause, so in their report they say the fire was likely sparked by an electrical fault.

Juby told The Fifth Estate that when he saw the wreckage after it was salvaged from the ocean he wondered what could have created so much heat. He said that was his first clue.

But Juby said high levels of magnesium — a key ingredient in an incendiary device — were discovered in the cockpit area. Several other investigators and a federal scientist who The Fifth Estate spoke to supported Juby's informed suspicions.

A year into the investigation metallurgist Dr. Jim Brown, using auger electron spectroscopy, discovered suspicious levels of magnesium — ten times the anticipated amount — and other elements associated with arson in melted wiring from the section of the plane that suffered the greatest fire damage.

"There was a lot of magnesium. More than I would have expected," he said.

Instead, the TSB was focused on the crash being the result of an accident. Any hint of criminal activity meant it would be forced to drop the probe and turn it over to the RCMP.

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.

Juby said the RCMP did not support his findings and that he was pressured to stop his own inquiries. He said the RCMP brass ordered him to remove any reference to magnesium or a suspected incendiary device from his investigative notes.

The Fifth Estate contacted other investigators with the TSB and the RCMP, who said they had encouraged Juby's search for the source of the magnesium, however they declined to go on camera.

The TSB told The Fifth Estate that they dismissed Brown's research because they considered it "bad science."

Juby said he has tried but failed to set the record straight inside the RCMP for years. He said the system failed too.

"If Canada can't follow through on 229 potential homicides, then you know, what happens when there's only one?" he said.