Forensic tests on the exhumed body of Yasser Arafat show that the level of polonium in his body was 18 times higher than normal.
The results are the first solid medical evidence to suggest the late Palestinian leader could have been deliberately poisoned with the rare radioactive substance.
Scientists in Switzerland have been testing Arafat’s remains since his body was exhumed in November last year, and have now confirmed polonium levels in Arafat’s ribs and pelvis were significantly higher than average.
They also discovered higher than expected levels of radiation in the soil around his body.
The findings, first revealed by Al Jazeera after the news organisation obtained an exclusive copy of the 108-page report, led Arafat’s widow Suha to declare his death a murder, adding “we are revealing a real crime, a political assassination”.
Ms Arafat went on: “This has confirmed all our doubts… It is scientifically proved that he didn't die a natural death and we have scientific proof that this man was killed”
She stopped short of specifically blaming anybody for her husband’s death however, acknowledging he had made many enemies during his time as the leader of the Palestinian Liberation Organization.
Allegations of foul play surfaced immediately after Arafat’s death in 2004. Despite having many foes among his own people, a large number of Palestinians quickly pointed the finger at Israel - the country that besieged Arafat in his Ramallah headquarters during the final years of his life.
The Israeli government has denied any role in his death, noting that he was 75 years old and had an unhealthy lifestyle.
An investigation by the Qatar-based Al Jazeera television news channel first reported last year that traces of polonium-210 were found on personal effects of Arafat given to his widow by the French military hospital where he died.
That led French prosecutors to open an investigation for suspected murder in August 2012 at the request of Suha Arafat. Forensic experts from Switzerland, Russia and France all took samples from his corpse for testing after the Palestinian Authority agreed to open his mausoleum.
The head of the Russian forensics institute, Vladimir Uiba, was quoted by the Interfax news agency last month as saying no trace of polonium had been found on the body specimens examined in Moscow, but his Federal Medico-Biological Agency later denied he had made any official comment on its findings.
The French pathologists have not reported their conclusions publicly, nor have their findings been shared with Suha Arafat's legal team. A spokeswoman for the French prosecutor's office said the investigating magistrates had received no expert reports so far.
One of her lawyers said the Swiss institute's report, commissioned by Al Jazeera, would be translated from English into French and handed over to the three magistrates in the Paris suburb of Nanterre who are investigating the case.
Professor David Barclay, a British forensic scientist retained by Al Jazeera to interpret the results of the Swiss tests, said the findings from Arafat's body confirmed the earlier results from traces of bodily fluids on his underwear, toothbrush and clothing.
“In my opinion, it is absolutely certain that the cause of his illness was polonium poisoning,” Barclay told the Reuters news agency. “The levels present in him are sufficient to have caused death.
”What we have got is the smoking gun - the thing that caused his illness and was given to him with malice.“
The same radioactive substance was slipped into a cup of tea in a London hotel to kill defecting Russian spy Alexander Litvinenko in 2006. From his deathbed, Litvinenko accused Russian President Vladimir Putin of ordering his murder.
The British government refused to hold a public inquiry into his death after ministers withheld some material which could have shed light on Russia's suspected involvement.
Barclay said the type of polonium discovered in Arafat's body must have been manufactured in a nuclear reactor.
While many countries could have been the source, someone in Arafat's immediate entourage must have slipped a miniscule dose of the deadly isotope probably as a powder into his drink, food, eye drops or toothpaste, he said.
Arafat fell ill in October 2004, displaying symptoms of acute gastroenteritis with diarrhoea and vomiting. At first Palestinian officials said he was suffering from influenza.
He was flown to Paris in a French government plane but fell into a coma shortly after his arrival at the Percy military hospital in the suburb of Clamart, where he died on November 11.
The official cause of death was a massive stroke but French doctors said at the time they were unable to determine the origin of his illness. No autopsy was carried out.
Barclay said no one would have thought to look for polonium as a possible poison until the Litvinenko case, which occurred two years after Arafat's death.
Some experts have questioned whether Arafat could have died of polonium poisoning, pointing to a brief recovery during his illness that they said was not consistent with radioactive exposure. They also noted he did not lose all his hair. But Barclay said neither fact was inconsistent with the findings.
Since polonium loses 50 percent of its radioactivity every four months, the traces in Arafat's corpse would have faded so far as to have become untraceable if the tests had been conducted a couple of years later, the scientist said.
”A tiny amount of polonium the size of a flake of dandruff would be enough to kill 50 people if it was dissolved in water and they drank it,“ he added.
The Al Jazeera investigation was spearheaded by investigative journalist Clayton Swisher, a former U.S. Secret Service bodyguard who became friendly with Arafat and was suspicious of the manner of his death.
Hani al-Hassan, a former aide, said in 2003 that he had witnessed 13 assassination attempts on Arafat's life, dating back to his years on the run as PLO leader. Arafat claimed to have survived 40 attempts on his life.
Arafat narrowly escaped an Israeli air strike on his headquarters in Tunisia in 1985. He had just gone out jogging when the bombers attacked, killing 73 people.
He escaped another attempt on his life when Israeli warplanes came close to killing him during the 182 invasion of Beirut when they hit one of the buildings they suspected he was using as his headquarters but he was not there.
In December 2001, Arafat was rushed to safety just before Israeli helicopters bombarded his compound in Ramallah with rockets.
Q. What is it?
Discovered by Marie Curie in the 19th century, polonium is a highly radioactive element, rarely found outside the military and scientific establishment. The particular isotope detected on Yasser Arafat's personal belongings – polonium 210 – occurs naturally in small concentrations in the environment. But high doses of the radioactive substance, which emits radiation in the form of alpha particles, can damage tissues and organs. These cannot pass through the skin, and to pose a danger polonium must be taken into the body, for example by eating it or breathing its radiation.
Q. Has it been used to poison people before?
Polonium hit the headlines in 2006, when it was used to kill the former Russian spy turned Kremlin critic Alexander Litvinenko. He died in November that year after falling suddenly ill in London. Subsequent tests found traces of radiation at various locations in London, and eventually linked Litvinenko's death to the presence of a large dose of polonium 210 in his body.
Q. How was Yasser Arafat linked to polonium?
Samples of clothes worn by the late Palestinian leader shortly before he fell ill were sent to a Swiss laboratory this year by the Al Jazeera television network, in co-operation with his widow and daughter. Scientists at the lab in Lausanne went on to discover significant traces of the radioactive element on his belongings.
Al Jazeera Investigates - What Killed Arafat? (July 2012)