The first forensic tests on samples taken from Yasser Arafat's corpse have shown unexpectedly high levels of radioactive polonium-210, suggesting the Palestinian leader could have been poisoned with the rare and lethal substance.

The Swiss scientists who tested Arafat's remains after the exhumation of his body in November 2012 discovered levels of polonium at least 18 times higher than usual in Arafat's ribs, pelvis and in soil that absorbed his bodily fluids.

The Swiss forensic report was handed to representatives of Arafat's widow, Suha Arafat, as well as representatives of the Palestinian Authority on Tuesday. A copy of the report was obtained exclusively by the al-Jazeera TV network, which shared it with the Guardian before publication.

The Swiss report said that even taking into account the eight years since Arafat's death and the quality of specimens taken from bone fragments and tissue scraped from his body and shroud, the results "moderately support the proposition that the death was the consequence of poisoning with polonium-210".

Suha Arafat said the evidence in the report suggested that her then healthy 75-year-old husband, who died in 2004 four weeks after he first fell ill following a meal, was almost certainly murdered by poisoning. She told al-Jazeera: "This is the crime of the century."

Speaking to the Guardian after receiving the report, she said she would press for answers on who was responsible. "It's shocking … I remember how Yasser was shrinking at the hospital, how in his eyes there were a lot of questions. Death is a fate in life, it is everybody's fate, but when it's poison it's terrible. We are mourning him again now."

With Zahwa, 18, her daughter by Arafat, she said she suspected a "conspiracy to get rid of him", adding: "My daughter and I have to know who did it. We will not stop in our quest to find out. I hope the Palestinian Authority goes further on it, searching every single aspect of it. It is of course a political crime." She said: "This is separate from the peace process or talks. Any judicial investigation is separate from the peace process."

David Barclay, a British forensic scientist who had studied the report, told al-Jazeera: "The report contains strong evidence, in my view conclusive evidence, that there's at least 18 times the level of polonium in Arafat's exhumed body than there should be."

He said the report represented "a smoking gun". Barclay said: "It's what killed him. Now we need to find out who was holding the gun at that time," adding: "I would point to him being given a fatal dose. I don't think there's any doubt at all."

The Israeli government, however, dismissed the report. "The Swiss findings are not conclusive," said Yigal Palmor, a foreign ministry spokesman.

"Even if they did find traces of polonium that could indicate poisoning, there's no evidence of how that poisoning occurred. Before the Palestinian Authority jumps to conclusions, there are many questions still to be answered.

"Israel is not involved in any way. There's no way the Palestinians can stick this on us. It's unreasonable and unsupported by facts. We will see yet another round of accusations, but there's no proof."

Dov Weissglass, a former aide to Ariel Sharon, the Israeli prime minister at the time of Arafat's death, also denied Israeli involvement. "To the best of my knowledge, we had no hand in this," he said, adding that neither the prime minister nor the Israeli security services had played any part in the Palestinian leader's demise.

"By the end of 2004, we had no interest in harming him. By then, Arafat was marginalised, his control over Palestinian life was minimal. So there was no logic, no reason."

Danny Rubinstein, a journalist and author of a book about Arafat, had a different memory of events. In the weeks and months before Arafat's death, he said, people in Sharon's inner circle talked constantly about how to get rid of him. "For me, it was very clear from the beginning. Every day this was the topic – should we expel him, or kill him, or bomb the Muqata [Arafat's HQ]. It was obvious to me that they would find a way."

Palmor said that among the scientists who tested Arafat's remains only the French team were independent. The Swiss were commissioned by Suha Arafat, and the Russians by the Palestinian Authority, he said. "These results should be taken with a few grains of salt. This story is still as mysterious as it was on day one."

Tawfik Tirawi, head of the Palestinian committee investigating Arafat's death, did not respond to a request from comment. But a senior Palestinian leader, Hanan Ashrawi, said: "This report confirms the suspicions that we've had all along. We know Arafat was killed, now we know how. And we know who had the means, the opportunity and the motive. Justice must now take its course."

Arafat died in a French military hospital on 11 November 2004,. He had been transferred there from his headquarters in the West Bank after his health deteriorated over weeks, beginning with severe nausea, vomiting, abdominal pain and diarrhoea around four hours after eating dinner on 12 October. French doctors have said he died of a massive stroke and had suffered from a blood condition known as disseminated intravascular coagulation, or DIC. But the records were inconclusive about what brought about the DIC. No autopsy was carried out.

Allegations that Arafat may have been poisoned emerged immediately after his death and the claim was raised again by al-Jazeera TV last summer, following a nine-month investigation culminating in the film What Killed Arafat?

Al-Jazeera said it was given access to a duffel bag of Arafat's personal effects by his widow, which it passed to a Swiss institute. Swiss toxicological tests on those samples including hair from a hat, saliva from a toothbrush, urine droplets on underpants and blood on a hospital hat found that the belongings had elevated traces of polonium-210, the lethal substance used to kill the Russian dissident Alexander Litvinenko.

The Swiss institute said Arafat's bones would have to be tested to get a clearer answer, warning that polonium decayed fast and an autopsy needed to be done quickly. In August last year, French prosecutors opened a murder inquiry into Arafat's death. In November, Arafat's corpse was exhumed from its mausoleum in Ramallah in the presence of three international teams of scientists: the Swiss team, a French team that was part of the Paris judicial investigation and a Russian team.

The Swiss team's report states that they carried out toxicological tests on Arafat's "almost skeletonised body along with residues from his shroud". The samples, including fragments of bones taken from his left ribs and pelvis as well as remnants of tissue from the abdominal cavity and grave soil, showed "unexpectedly high" activity of polonium-210.

Suha Arafat's lawyer, Saad Djebbar, told the Guardian the Swiss report was "evidence that there was a crime committed". He said he had handed the Swiss report to French investigators, whose inquiry is ongoing. French scientists conducted their own tests as part of the legal investigation but have not published findings as the inquiry continues.

Arafat's daughter, Zahwa, a student of international relations in Malta, told the Guardian: "I want to find out who did it and their motive for doing it." She said she trusted the French investigation to shed light on that.