However, they could not say whether polonium poisoning had caused his death in 2004.
Their report concluded that Yasser Arafat’s remains showed levels of polonium 18 times higher than normal.
Many Palestinians have long believed that Israel poisoned Yasser Arafat. There have also been allegations that he had AIDS or cancer. Israel has consistently denied any involvement.
The scientists – from the Vaudois University Hospital Centre (CHUV) in Lausanne, Switzerland – had carried out a detailed examination of Arafat’s medical records, samples taken from his remains and items he had taken into the hospital in Paris where he died in 2004.
The biological materials included pieces of Yasser Arafat’s bones and soil samples from around his corpse.
Professor Francois Bochud told a news conference on Thursday that the high level of polonium detected “by definition… indicates third party involvement… Our results offer moderate backing for the theory of poisoning.”
But he went on to say: “Was polonium the cause of the death for certain? The answer is no, we cannot show categorically that hypothesis that the poisoning caused was this or that.”
In their report, the scientists had stressed that they had been unable to reach a more definitive conclusion because of the time that had lapsed since Yasser Arafat’s death, the limited samples available and the confused “chain of custody” of some of the specimens.
Polonium-210 is a highly radioactive substance. It is found naturally in low doses in food and in the body, but can be fatal if ingested in high doses.
Yasser Arafat, who led the Palestine Liberation Organization for 35 years and became the first president of the Palestinian Authority in 1996, fell violently ill in October 2004 at his compound in the West Bank.
Two weeks later Yasser Arafat was flown to a French military hospital in Paris, where he died on November 11, 2004, aged 75.
His official medical records say he died from a stroke resulting from a blood disorder.
France began a murder inquiry in August 2012 after the preliminary findings of polonium by the Lausanne scientists, who have been working with an al-Jazeera documentary crew.
Parallel investigations are being carried out by French and Russian experts – one Russian official said last month that no traces of polonium had been found.
Ysser Arafat’s widow, Suha Arafat, who had objected to a post-mortem at the time of his death, agreed for his body to be exhumed a year ago “to reveal the truth”.
Welcoming the Swiss report, Suha Arafat said she had no doubt that her husband had been assassinated but refused to point the finger at Israel.
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