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Theories about the cause of death

Numerous theories have circulated regarding Arafat's death, with the most prominent being poisoning (possibly by polonium) and AIDS -related illnesses, as well as liver disease or a platelet disorder.

In September 2005, an Israeli AIDS expert claimed that Arafat bore all the symptoms of AIDS based on obtained medical records. But others, including Patrice Mangin of the University of Lausanne and The New York Times, disagreed with this claim, insisting that Arafat's record indicated that it was highly unlikely that the cause of his death was AIDS. Arafat's personal doctor Ashraf al-Kurdi and aide Bassam Abu Sharif maintained that Arafat was poisoned, possibly by thallium. A senior Israeli physician concluded that Arafat died from food poisoning. Both Israeli and Palestinian officials have denied claims that Arafat was poisoned. Palestinian foreign minister Nabil Shaath ruled out poisoning after talks with Arafat's French doctors.

On 4 July 2012, Al Jazeera published the results of a nine-month investigation, which found that rumors Arafat had died of cancer, cirrhosis, or AIDS were not true, because he was in good health until he fell ill suddenly on 12 October 2004 – but revealed that tests carried out by Swiss experts found traces of polonium in quantities much higher than could occur naturally on Arafat's personal belongings. On 12 October 2013, the British medical journal The Lancet published a peer-reviewed article by the Swiss experts about the analysis of the 38 samples of Arafat's clothes and belongings and 37 reference samples which were known to be polonium-free, suggesting that Arafat could have died of polonium poisoning.

On 27 November 2012, three teams of international investigators, a French, a Swiss, and a Russian team, collected samples from Arafat's body and the surrounding soil in the mausoleum in Ramallah, to carry out an investigation independently from each other.

On 6 November 2013, Al Jazeera reported that the Swiss forensic team had found levels of polonium in Arafat's ribs and pelvis 18 to 36 times the average, even though by this point in time the amount had diminished by a factor of 2 million. François Bochud, the head of the Swiss team, said that the poisoning hypothesis by polonium is "reasonably supported", while forensic scientist Dave Barclay, retained by Al Jazeera, stated, "In my opinion, it is absolutely certain that the cause of his illness was polonium poisoning.... What we have got is the smoking gun – the thing that caused his illness and was given to him with malice." Derek Hill, a professor in radiological science at University College London who was not involved in the investigation, said "I would say it's clearly not overwhelming proof, and there is a risk of contamination (of the samples), but it is a pretty strong signal.... It seems likely what they're doing is putting a very cautious interpretation of strong data."

But on 26 December 2013, a team of Russian scientists released a report saying they had found no trace of radioactive poisoning—a finding that came after the French report found traces of polonium. Vladimir Uiba, the head of the Federal Medical and Biological Agency, said that Arafat died of natural causes and the agency had no plans to conduct further tests. Unlike the Swiss report, the French and Russian reports were not made public at the time. The Swiss experts read the French and Russian reports and argued that the radiologic data measured by the other teams supported their conclusions of a probable death by polonium poisoning. In March 2015, a French prosecutor closed a 2012 French inquiry, stating that French experts maintained that the polonium and lead traces found were of an environmental nature. Palestinian official Wasel Abu Yousef said of the 2013 report, "The French report is politicized and is contrary to all the evidence which confirms that the president was killed by poisoning", and "This report is an attempt to cover up what happened in Percy hospital."