Palestinian investigators said on Friday that Israel is the "only suspect" in the death of president Yasser Arafat, after laboratory tests suggested he died from polonium poisoning."We say that Israel is the prime 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," Palestinian inquiry chief Tawfiq Tirawi told a news conference in the West Bank city of Ramallah.Tirawi said the Palestinian inquiry had studied the findings of Swiss scientists, released Wednesday, which "moderately" supported the notion that Arafat had been poisoned."This is the crime of the 21st century," Tirawi said. "The fundamental (goal) is to find out who is behind the liquidation of Yasser Arafat."Palestinian officials on Thursday demanded an international inquiry into Arafat's "killing.""The results prove Arafat was poisoned by polonium," said senior Palestine Liberation Organization official Wasel Abu Yusef. "This substance is owned by states, not people, meaning that the crime was committed by a state," he told AFP, calling for an "international committee" to probe the killing along the lines of the one that investigated the murder of Lebanon's Rafiq Hariri.Speaking to reporters in Lausanne Thursday, the Swiss team said the test results neither confirmed nor denied that polonium was the actual source of his death, although they provided "moderate" backing for the idea he was poisoned by the rare and highly radioactive element.They said the quantity of the deadly substance found on his remains pointed to the involvement of a third party."We can't say that polonium was the source of his death ... nor can we rule it out," said Professor Francois Bochud of the Lausanne Institute of Applied Radiophysics.Bochud's lab measured levels of polonium up to 20 times higher than it is used to detecting.Arafat died in France on November 11, 2004 at the age of 75 after falling sick a month earlier, but doctors were unable to specify the cause of death and no post-mortem was carried out at the time.In November 2012, his remains were exhumed and samples taken, partly to investigate whether he had been poisoned with polonium - a suspicion that grew after the assassination in that manner of Russian ex-spy and Kremlin critic Alexander Litvinenko in London in 2006.Since Arafat's death, Palestinian society has long given currency to the rumor that he was murdered, with Israel the party most often blamed.But there has never been any proof.