Q&A: Investigation into Yasser Arafat's death
Palestinian President Yasser Arafat died in hospital in France in November 2004, weeks after falling ill at his compound in the West Bank city of Ramallah. French doctors said Arafat had an unidentified blood disorder and gave the cause of death as a stroke. Since then there have been allegations that Arafat was poisoned, possibly with the radioactive element, polonium-210. A series of investigations has been trying to establish whether he was murdered.
How did Arafat die?
In 2005, the New York Times obtained a copy of Arafat's medical records from two Israeli journalists, Avi Isacharoff and Amos Harel, who had been given them by a senior Palestinian official.
According to the records, the 75-year-old's illness began four hours after he ate a meal on the evening of 12 October 2004 inside the Muqataa presidential compound in Ramallah. Israeli forces had kept him isolated there for three years, accusing him of sponsoring a wave of deadly attacks by Palestinian militants.
For the next two weeks, he vomited and had abdominal pain and diarrhoea, but did not have a fever. He became stuporous and lost 3kg (6.6lb), according to the records. He was seen by a team of Palestinian, Egyptian, Jordanian and Tunisian doctors, and was treated for flu and thrombocytopenia, an abnormally low blood platelet count.
The records indicated that Arafat did not receive antibiotics until 27 October - 15 days after the onset of his illness. Two days later he was flown by helicopter to Jordan and then private jet to the Percy Military Training Hospital in Clamart, outside Paris.
It was only once Arafat arrived in Paris that he was diagnosed with a serious blood disorder - disseminated intravascular coagulation (DIC) - which the French doctors were never able to control and which led to his death.
Arafat did improve for a time at Percy hospital, but he slipped into a coma on 3 November, when he was moved to intensive care. He had massive haemorrhagic stroke on 8 November and died three days later.
Why do people think he was poisoned?
Many senior Palestinian officials claim that Arafat was poisoned by Israel.
Israel's prime minister at the time of Arafat's death, Ariel Sharon, saw the Palestinian leader as a terrorist and an obstacle to peace.
In 2002, Mr Sharon told the Maariv newspaper that he regretted not "eliminating" Arafat during the invasion of Lebanon in 1982. But he also stressed that Israel had later made a "commitment" not to harm him.
However, Mr Sharon is alleged to have told former US President George W Bush in April 2004 that he no longer felt bound by this promise.
Israel has strenuously denied that it had anything to do with Arafat's death.
On 8 November 2013, Israeli Foreign Ministry spokesman Yigal Palmor told the BBC: "I will state this as simply and clearly as I can: Israel did not kill Arafat, period. And that's all there is to it. The Palestinians need to stop levelling these accusations without a shadow of proof. Enough is enough."
What do Arafat's medical records say?
Despite extensive testing, the French doctors never discovered the specific cause of the infection that led to the DIC, according to the medical records obtained by the New York Times.
Biopsies performed did not show evidence of any infectious agent or cancer, the records state. Tests carried out by a laboratory in Tunis on cultures of blood, stool, urine and bone marrow were also negative.
Specimens were sent to three laboratories for standard toxicology tests to detect metals and drugs, but none were found.
No post-mortem was performed because Arafat's widow, Suha, did not request one. The Palestinian Authority also chose not to ask for the procedure because they felt it would "turn what is a martyrdom case into a police criminal case", senior Fatah official Nabil Shaath told al-Jazeera.
Independent Israeli and American experts who reviewed Arafat's records told the New York Times that it was highly unlikely that he was poisoned. They said he did not suffer the extensive kidney and liver damage they would expect from a poison, although he did have jaundice.
They also said the course of his illness and pattern of his symptoms also made rumours that he died of Aids improbable.
Al-Jazeera published in July 2012 what it said was a copy of Arafat's bacteriology report from the Percy military hospital. The records state that blood samples screened using the ELISA test came back as "negative" for HIV antigens. That suggests Arafat did not have Aids, though experts caution that it is possible for people with early HIV infection to produce a negative ELISA test result.
Why was Arafat exhumed?
On 3 July 2012, an al-Jazeera documentary reported the results of a nine-month investigation that had tried to discover what killed Arafat.
It said that scientists at the Institute of Radiation Physics (IRA), which is part of Switzerland's respected Vaudois University Hospital Centre, had found "significant" traces of a highly radioactive and toxic material on personal effects given to his widow after his death, including his trademark keffiyeh.
Francois Bochud, the director of the institute, said its tests had found an "unexplained, elevated amount of unsupported polonium-210 in the belongings of Mr Arafat that contained stains of biological fluids".
To test the theory that Arafat was poisoned by polonium-210 it would be necessary to exhume and analyse his remains, Dr Bochud added.
Suha Arafat subsequently confirmed that she would submit a request to the Palestinian Authority, telling al-Jazeera: "We have to go further and exhume Yasser Arafat's body to reveal the truth."
Mrs Arafat also filed a civil suit at a court in the Paris suburb of Nanterre, alleging that her husband was murdered by an unnamed "perpetrator X". French prosecutors began a murder inquiry in August 2012.
The Palestinian Authority welcomed the decision and granted French investigators and the Swiss scientists permission to exhume Arafat's body and take samples for testing. Russia also sent experts, and samples were sent to its Federal Medico-Biological Agency.
What did tests on Arafat's body show?
On 6 November, al-Jazeera revealed the findings of 10 experts at the Vaudois University Hospital Centre (CHUV) in Lausanne. British forensic scientist David Barclay told al-Jazeera that at least 18 times the normal level of polonium-210 had been found in Arafat's rib.
"New toxicological and radio-toxicological investigations were performed, demonstrating unexpectedly high levels of polonium-210 and lead-210 activity in many of the analysed specimens" taken from Arafat's ribs, pelvis and soil that had absorbed his bodily fluids, the report said.
At a news conference to explain their findings, Francois Bochud said such high levels of polonium, "by definition... indicates third party involvement... Our results offer moderate backing for the theory of poisoning".
But he added a note of caution: "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."
The report had noted four "particular critical problems" - the lack of adequate biological specimens, partly because samples taken during Arafat's hospitalisation were destroyed; the very small size of the specimens made analysis and interpretation of the results difficult; the length of time between the death and the investigations, which contributes to the uncertainty of the interpretation of the results; and the incomplete "chain of custody" for the bag of personal affects analysed in 2012.
On 8 November, the medical expert on the Palestinian committee investigating Arafat's death quoted a separate report by the Russian Federal Medico-Biological Agency.
"The outcome of the comprehensive report on the levels of polonium-210 and the development of his illness does not give sufficient evidence to support the decision that polonium-210 caused acute radiation syndrome leading to death," said Dr Abdullah Bashir.
However, doubts were raised about the Russian report later that day by al-Jazeera, which said it had obtained a copy. Experts who reviewed the 15-page document told al-Jazeera that the results were "inconclusive". The Russian exhumation team had received 20 samples from Arafat's remains, but the scientists appeared to have only been given four samples to test - two from the skull and two from "extremity bones", it showed.
Dr Bochud said the skull "would not be the best kind of bone sample to measure" because it was not vascularised, while Mr Barclay said the levels of plutonium-210 found on the four specimens "appear to be 10 or 20 times less than you'd expect just from anyone else in the world". A source who leaked the report claimed the Russian foreign ministry had issued "clear instructions" to the Federal Medico-Biological Agency scientists on "how the final report should look like".
What does the Palestinian investigative committee allege?
On 8 November, the Palestinian investigative committee told a news conference in Ramallah that Israel was the "the prime, fundamental and only suspect in the case of Yasser Arafat's assassination".
Despite the conclusion of the Russian scientists' report, Dr Bashir noted they had still found "large amounts" of polonium in Arafat's remains, and said that further "supports our theory" that he did not die of disease or old age, "but rather by poisonous material".
The head of the Palestinian committee, Gen Tawfik Terawi said: "It is not important that I say here that he was killed by polonium... But I say, with all the details available about Yasser Arafat's death, that he was killed and that Israel killed him."
Gen Terawi, an intelligence chief at the time of Arafat's death, did not present evidence of Israeli involvement, other than what he said were "statements by Israeli leaders who at the time said that Yasser Arafat should go, and should disappear". He dismissed as "rumours" speculation that members of Arafat's entourage killed him, saying he dealt only in facts.
"We say that Israel is the prime, fundamental and only suspect in the case of Yasser Arafat's assassination, and we will continue to carry out a thorough investigation to find out and confirm all the details and all elements of the case," Gen Terawi added.
Israel's government dismissed any suggestion that it was involved.
What is polonium-210?
It is a naturally occurring radioactive material that emits highly hazardous alpha (positively-charged) particles. The substance, historically called radium F, was first discovered by Marie Curie in the 19th Century.
There are very small amounts of polonium-210 in the soil and in the atmosphere, and everyone has a small amount of it in their body. But in high doses it damages tissues and organs.
It cannot pass through the skin, and must be ingested or inhaled.
Although polonium-210 occurs naturally, acquiring enough of it to kill someone would require individuals with expertise and connections. They would need sophisticated lab facilities - and access to a nuclear reactor. Alternatively, it could be obtained from a commercial supplier.
The former Russian spy Alexander Litvinenko died of exposure to polonium-210 in London in 2006. The UK authorities have accused Andrei Lugovoi, an ex-KGB officer, of poisoning his tea.
The scientists from Lausanne have stressed caution over their findings, because polonium is a very unstable element with a half-life of 138 days. This means that after four months, the amount of polonium in a sample would have halved; after a year there would be just one eighth of the original amount.
Since Arafat was exhumed eight years after he died, only a tiny fraction of polonium would remain.