Swiss professor Francois Bochud, left, director of the Chuv Radiophysics Institute, IRA, and Swiss professor Patrice Mangin, right, director of the University Center of Legal Medicine in Lausanne, CURML, speak on a forensics report concerning the late President Yasser Arafat during a press conference at the Centre Hospitalier Universitaire Vaudois, CHUV, in Lausanne, Switzerland, Thurday, Nov. 7, 2013. Swiss, French and Russian teams took samples of the remains after exhuming Arafat's body in Ramallah, and submitted results to the Palestinian Authority on Nov. 5. AP Photo/Keystone, Laurent Gillieron Swiss professor Francois Bochud, left, director of the Chuv Radiophysics Institute, IRA, and Swiss professor Patrice Mangin, right, director of the University Center of Legal Medicine in Lausanne, CURML, pose with a forensics report concerning the late President Yasser Arafat during a press conference on of the Centre Hospitalier Universitaire Vaudois, CHUV, in Lausanne, Switzerland, Thurday, Nov. 7, 2013. A forensics report concerning the late President Yasser Arafat is presented during a press conference of the Centre Hospitalier Universitaire Vaudois, CHUV, in Lausanne, Switzerland, Thurday, Nov. 7, 2013. Palestinian Hanadi Kharma, paints a mural depicting the late Palestinian leader Yasser Arafat in the West Bank city of Nablus, Thursday, Nov. 7, 2013. AP Photo/Nasser Ishtayeh LAUSANNE, Switzerland LAUSANNE, Switzerland (AP) - Palestinian leader Yasser Arafat ingested lethal radioactive polonium before his death nine years ago and had high levels of it in his body that could not have been accidental, Swiss scientists confirmed Thursday. The Swiss lab examined Arafat's remains, his underclothes and a travel bag that he had with him in the days before his 2004 death in a Paris hospital. They found that the amounts of polonium and its byproduct lead in those items could not be naturally occurring. The timeframe of his illness and death were also consistent with polonium poisoning, they said. "You don't accidentally or voluntarily absorb a source of polonium - it's not something that appears in the environment like that," Patrice Mangin, director of the Lausanne University Hospital's forensics center, said at a news conference. He said he could not say unequivocally what killed Arafat since the biological samples obtained just last year were too degraded to determine the cause of death. "Our results reasonably support the poisoning theory," said Francois Bochud, director of the Institute of Radiation Physics that carried out the probe, though he was careful to emphasize the lingering questions that will require further investigation to answer. Can we exclude polonium as cause of death? The response is clearly 'no,'" he told reporters. Was polonium the cause of the death for certain? The answer is no. Asked if there were any innocent explanations left to explain the high level of polonium, Bochud told The Associated Press that other theories were tested, such as the presence of radon gas or radium, and each one was ruled out. "We tried hard to imagine all the possibilities," he said. Mangin said he could not imagine a scenario in which Arafat could have been accidentally poisoned. I think we can eliminate this possibility because as you can imagine, you cannot find polonium everywhere. It's a very rare toxic substance," he told the AP. The Palestinian leader died in November 2004 at a French military hospital, a month after falling violently ill at his Israeli-besieged West Bank compound. Palestinian officials have alleged from the start that Israel poisoned Arafat, a claim Israel denies. Bochud said just a minuscule amount of polonium slipped into food or drink would be lethal within about a month. Arafat's body was exhumed earlier this year. When they did open the tomb, they saw a skeleton, Mangin said. The Swiss report said Arafat's remains and the burial soil contained elevated levels of polonium-210. Suha Arafat, his widow, called on the Palestinian leadership Thursday to seek justice for her husband. Speaking to The Associated Press by phone from the Qatari capital Doha, she did not mention Israel, but argued that only countries with nuclear capabilities have access to polonium. "I can't accuse anyone, but it's clear this is a crime, and only countries with nuclear reactors can have and do that," she said. Now the ball is in the hands of the Palestinian Authority. They have to find the tools and pursue the legal case. Scientists not connected to the study said polonium is not naturally found in the human body. "It's quite difficult to understand why (Arafat) might have had any polonium if he was just in his headquarters in Ramallah," said Alastair Hay, a professor of environmental toxicology at the University of Leeds. He wasn't somebody who was moving in and out of atomic energy plants or dealing with radioactive isotopes. Still, Derek Hill, a radiation expert at University College London, noted the polonium findings could have been the result of contamination. The Swiss scientists said in their report they could not account for the "chain of custody" of the specimens between Arafat's death and when they were received in Lausanne last February. But this was for his underclothes and travel bag, which were used for an initial and less conclusive report in The Lancet. The scientists' second, 108-page report on the findings, which were presented at the news conference, were based on further testing on Arafat's body. Asked whether the polonium findings on Arafat's remains could have been the result of contamination, Bochud told AP, "I think this can really be ruled out. Because it was really difficult to access the body.... when we opened the tomb, we were all together. Israeli officials vehemently denied any role in Arafat's death. Paul Hirschson, a Foreign Ministry spokesman, dismissed the allegations as "hogwash." Former Israeli official Dov Weisglass said Israel had no motive to kill Arafat at a time when he had been sidelined and isolated at his West Bank compound. "I can assure you that officially, Israel had nothing to do with it," Weisglass, a senior adviser to then-Israeli Prime Minister Ariel Sharon, said in a phone interview. In late 2004, Israel had no reason whatsoever even to consider a step of this kind. Polonium first hit the headlines when it was used to kill KGB agent-turned-Kremlin critic Alexander Litvinenko in London in 2006. It can be a byproduct of the chemical processing of uranium, but usually is made artificially in a nuclear reactor or a particle accelerator. In a statement by his office, Palestinian President Mahmoud Abbas urged official Palestinian bodies to "follow up the investigation and to reveal all the facts about the death of the late leader Yasser Arafat, and to put the whole truth before the Palestinian people and the world." The investigation was seen as potentially embarrassing to Abbas and his inner circle. The Palestinian investigation quickly hit a dead end. Abbas must now show publicly that he is interested in a vigorous follow-up, while not disrupting his negotiations with Israel. The U.S. wants Israel and the Palestinians to keep negotiating, even though there appears to be no visible progress in peace talks after more than three months of meetings. Abbas was in the Jordanian capital Amman on Thursday for a meeting with U.S. Secretary of State John Kerry. Associated Press writers Mohammed Daragmen in Ramallah, West Bank, Daniel Estrin in Jerusalem and Lori Hinnant in Paris, and AP Medical Writer Maria Cheng in London contributed to this report.