Israel is the only suspect in the 2004 death of Yasser Arafat, the chief Palestinian investigator in the case alleged Friday, a day after Swiss scientists said the Palestinian leader was probably poisoned by radioactive polonium.
The investigator, Tawfik Tirawi, said the probe would continue, but did not say what more the Palestinians could do to try to solve the mystery.
He did not present evidence of Israeli involvement, arguing only that Israel had the means and motive to do so. Israel has repeatedly denied it was behind Arafat's death, and did so again Friday, in light of the new allegations.
Arafat's widow, Suha, has called on the Palestinians to seek an international investigation or legal action, but Tirawi said such a decision is up to the Palestinian leadership. Arafat's successor, President Mahmoud Abbas, has so far not commented on the substance of the Swiss team's findings.
Arafat's grave was opened earlier this year, enabling Swiss, Russian and French scientists to take samples of remains and burial soil for separate investigations. At Friday's news conference, Palestinian investigators summarized the findings of the Russian experts, whom Abbas had asked for a separate probe.
Dr. Abdullah Bashir, the medical expert on the Palestinian team, said the Russian scientists did not find sufficient evidence to determine that "polonium-210 caused the radiation that led to the death." He did not elaborate.
However, both teams determined that Arafat did not die of disease or old age, "but rather, by poisonous material," Bashir said, adding that "this supports our theory."
The Russians were also looking at the possibility of other poisons, Bashir said, adding that more study was required.
Tirawi, meanwhile, was evasive when asked repeatedly whether he believed Arafat was killed by polonium.
"It is not important that I say here that he was killed by polonium," he said. "But I say, with all the details available about Yasser Arafat's death, that he was killed, and that Israel killed him."
At another point, Tirawi described Israel as the "first, fundamental and only suspect in the assassination of Yasser Arafat."
Israel has denied any role in Arafat's death, saying it had politically isolated him at the time and had no reason to assassinate him.
"Let me state this as simply as I can: Israel did not kill Arafat," Israeli Foreign Ministry spokesman Yigal Palmor said Friday.
"The Palestinians should stop this nonsense and stop raising these baseless accusations without any shadow of proof," Palmor added.
Arafat died on Nov. 11, 2004 at a French military hospital, at the age of 75, a month after falling ill at his West Bank compound. At the time, French doctors said he died of a stroke and had a blood-clotting problem, but records were inconclusive about what caused that condition.
After his death, Palestinians launched their own investigation, questioning dozens of people in Arafat's headquarters, including staff and bodyguards, but no suspects emerged.
Security around Arafat was easily breached toward the end of his life, a time when he was holed up in his Israeli-besieged compound. Aides have described him as impulsive, unable to resist tasting gifts of chocolate or trying out medicines brought by visitors from abroad.
Tirawi said Friday that the investigation encompassed hundreds of statements from Palestinians and non-Palestinians in the West Bank and around the world.
The investigation was dormant until the satellite TV station Al-Jazeera persuaded Arafat's widow last year to hand over a bag with her husband's underwear, headscarves and other belongings.
After finding traces of polonium in biological stains on the clothing, investigators dug up his grave in his Ramallah compound.
The Swiss scientists said Thursday that they found elevated traces of polonium-210 and lead in Arafat's remains, and that the timeframe of Arafat's illness and death was consistent with poisoning from ingesting polonium.
"Our results reasonably support the poisoning theory," said Francois Bochud, director of Switzerland's Institute of Radiation Physics.
France is conducting its own investigation into Arafat's death at the request of his widow, but no results have been released.
Polonium is rare and lethal even in minuscule amounts, and nine years on, it would be difficult to track down anyone who might have slipped it into Arafat's food or drink.
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.