A team of Swiss scientists released a report announcing findings that "moderately support the proposition" that Arafat was killed using the radioactive substance polonium-210.
Arafat's body was exhumed after the substance was found on the belongings he had with him at the French military hospital where he died. Separate teams of Russian and French scientists are also investigating the claims.
Suha Arafat, the leader's widow, said the news was difficult to take, but she was determined to find who killed her husband.
"I am mourning Yasser again," she said. "I don't know who did it."
While there have long been questions over Arafat's death -- and suspicions he was assassinated by either Israelis or Palestinian rivals to his authority -- the new evidence does little to answer those broader questions.
"We need to know who planned, who instigated, who implemented" the assassination, said Ghassan al-Shaka'a', a member of the Palestinian Liberation Organization's Executive Committee.
A spokesman for Israel's foreign ministry, Yigal Palmor, reiterated Israel's constant denial of invovlement.
The Swiss results were "inconclusive at best," Palmor said, adding that Suha Arafat "understands the evidence is so scant she cannot point the finger at anybody."