The death of Palestinian leader Yasser Arafat was likely a murder caused by poisoning, a Swiss forensics team has concluded. A report obtained and published by Al Jazeera describes how scientists cross-referenced medical records, personal effects, and samples from the exhumed body of Arafat to solve the mystery of his death nearly ten years after the fact. The exact cause, they say, was radioactive polonium-210, the same rare poison used in the killing of former Russian secret service officer Alexander Litvinenko in 2006.

Arafat's health problems, described by the report, started on October 12th, 2004, when he fell ill a few hours after eating dinner. After an initial diagnosis of flu, his symptoms progressively worsened, accompanied by neurological deterioration, acute renal failure, and eventually the cerebral hemorrhage that led to his death on November 11th in a French hospital. With no official cause released, his death was described in newspapers as the result of old age or a mysterious intestinal and blood disorder, and no autopsy was performed. Samples of blood, stool, and spinal fluid were sent to laboratories, but destroyed after an initial analysis.

By the time the investigation began, Arafat had been dead for seven years

But in 2011, Al Jazeera began an investigation of his death, during which Arafat's widow gave them access to medical records, as well as a travel bag that contained clothing worn before his death. The Swiss team took samples of the clothing, including some with blood and urine stains which, after analysis, showed signs of elevated polonium levels. With a relatively small chance that the items had been contaminated since Arafat's death, the team concluded that poisoning was a definite possibility. Al Jazeera used the results in a 2012 documentary on Arafat's death, and after the broadcast, French officials began a murder investigation that led to Arafat's remains being exhumed later that year.

From there, investigators were able to take hair, skin, and bone samples from his nearly skeletonized body. While the polonium would have decayed significantly in the eight years since Arafat's death, unusually high levels were found in bone samples and in dirt that was stained as his body decayed. Along with other evidence, this "moderately supports" the theory of polonium poisoning: the team gives Al Jazeera an 83 percent confidence level. What's still a mystery, though, is who was responsible. Israel is an obvious possibility: the year before Arafat's death, the Israeli deputy prime minister said that killing him was "one of the options" for reducing violence within its borders. But it's consistently denied involvement, and Al Jazeera says that there's still no evidence it was implicated. And after almost a decade, figuring out a culprit could prove much harder than finding a cause of death.