The Swiss lab examined Arafat's remains and his underclothes and a travel bag that he had with him in the days before his death in a Paris hospital and found that the polonium and lead amounts 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," said Patrice Mangin, director of the Lausanne University Hospital's forensics center. He said he could not say unequivocally what killed Arafat - the biological samples obtained just last year were far 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 said. "Was polonium the cause of the death for certain? The answer is no."
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.
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. They can resort to international legal institutions and international courts," she added.
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."
Derek Hill, a radiation expert at University College London, pointed out however that the polonium findings could have been the result of contamination.
"Somebody might have tried to doctor the evidence for their own political objectives," he said.
The Swiss scientists noted 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.
Bochud said polonium can be obtained with authorization, noting that his own lab receives it in liquid form for research.
In that form, he said, just a minuscule amount slipped into food or drink would be lethal within about a month.
The 108-page report on the findings was published Wednesday by the Qatar-based satellite TV station Al-Jazeera. The station, along with Mrs. Arafat, had initiated the renewed investigation of Arafat's death last year.
Arafat's body was exhumed earlier this year. The Swiss report said his remains and the burial soil contained elevated levels of polonium-210.
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. Israel has a nuclear research center and is widely believed to have a nuclear arsenal, but remains ambiguous about the subject.
Mrs. Arafat said the Swiss experts told her that had the remains been examined a year later, traces of polonium would have vanished.
In a statement put out 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 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.
On Friday, the Palestinian committee that has been investigating Arafat's death was to hold a news conference.
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.