* Swiss expert: French conclusion based on weak arguments
* French forensic report: No evidence of polonium poisoning
* Palestinian leader died after taking ill following a meal
By Stephanie Nebehay
GENEVA, Dec 5 (Reuters) - A Swiss scientist who examined samples from the body of former Palestinian leader Yasser Arafat said French experts had made weak arguments in concluding that he could not have died of poisoning in 2004.
French forensic examiners commissioned by magistrates investigating Arafat's death in a Paris hospital assessed on Tuesday that he had not been killed with radioactive polonium found in abnormally high levels in his body and clothing.
The Swiss approach resembled that of the French inquiry but dug deeper into the mystery, said Francois Bochud, director of the institute of radiation physics at University Hospital of Lausanne (CHUV) who helped exhume Arafat's remains a year ago.
"The basic measurement is the same as the French. When we tried to explain the origin of what we have observed we arrived at different conclusions because we went further," Bochud told Reuters. "We are in agreement except the French say the polonium was deposited by radon, but it a very weak argument."
The report of Russian experts who also took part in the exhumation has not been published but a Palestinian investigator has quoted it as saying there was insufficient evidence to support a poisoning theory.
Arafat, who signed the 1993 Oslo interim peace accords with Israel but then led an uprising after subsequent talks broke down in 2000, died aged 75 in November 2004.
His death came four weeks after he fell ill following a meal, suffering from vomiting and stomach pains, in his Ramallah compound while surrounded by Israeli tanks.
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.
SHROUDED IN MYSTERY
Both Swiss and French teams found high levels of polonium-210 and lead-210 in Arafat's remains, with 20 times the normal level in his bones.
Three possible explanations were advanced: his smoking, his use of weapons or equipment with luminous paint containing radium, and the presence of radon gas in his tomb.
Bochud said, however, that smoking could not have caused such high levels of polonium-210 and lead-210, there was no trace of radium and the levels of radon - a gas found naturally in the air and soil - were no different in Arafat's tomb from any other.
"But we did a lot of other investigations to rule out radon," he said. "We cleaned the bones chemically and physically in order to exclude contamination from the tomb. We and the French did this.
"We arrived at the conclusion that you could not explain the elevated level of polonium 210 and lead 210 by the presence of radon. We excluded radon as an origin of elevated values we measured, whereas the French say there was radon in the tomb and that explains the elevated level.
"This is exactly the point where we differ."
Both investigations also found 17 times more polonium-210 and lead-210 in the soil just below the body, where it had been "dirtied by the presence of his biological liquids", than further away from it, he said.
In addition, the Swiss compared readings from Arafat's shroud with those from his scalp, which were 13 times higher.
"So once again, if everything is explainable by the presence of radon, why did we measure much higher activity on the scalp than the shroud?" Bochud said.
Comparison of the remains with radioactive decay found in a commercial sample of polonium gave "a plausible explanation of what we found," he said.
There are few known cases of polonium poisoning. The most famous was that of defecting Russian spy Alexander Litvinenko, who drank a poisoned cup of tea in a London hotel in 2006.
The French conclusions were immediately challenged by his widow, Suha Arafat, who has argued that the death was a political assassination by someone close to her husband.
"We have no doubt that the most comprehensive and thorough report that examined all aspects of this case remains the Swiss report," Suha Arafat's lawyer Saad Djebbar told Reuters on Tuesday, calling it "the only show in town".
Many Palestinians believe Israel killed its longtime nemesis Arafat - a charge Israel denies. (Reporting by Stephanie Nebehay, writing by Tom Miles; editing by Mark Heinrich)