The findings are unlikely to resolve the persistent mystery of what — or who — killed the Palestinian leader in 2004 after weeks of illness.
"Can we exclude polonium as cause of death? The response is clearly no. Was polonium the cause of the death for certain? The answer is no," said Francois Bochud, one of the scientists at Vaudois University Hospital Centre in Lausanne, Switzerland who examined Arafat's remains.
The uncertainty is likely to feed the industry of conspiracy theorists that has thrived since Arafat's death at age 75. For many Palestinians, the belief that Israel assassinated him is a virtual certainty — a charge Israel has denied.
In a press conference Friday morning in the West Bank city of Ramallah, Palestinian Authority investigators maintained that Israel "is the prime and only suspect in the case of Yasser Arafat's assassination." They vowed to continue a full investigation into "who is behind the liquidation of Yasser Arafat."
Polonium-210 is a rare radioactive substance, toxic in high dosages but naturally present in the body in trace amounts.
More from GlobalPost: Polonium, HIV or 'Palestinium' — the real story of Yasser Arafat’s death
Suha Arafat, the leader's widow, claims the results of the Swiss tests — which found Arafat's remains contained levels of polonium 18 times higher than average — prove her husband was murdered, possibly by close associates.
The findings come as no surprise to Matthew Kalman, the co-author of an e-book published earlier this year, “The Murder of Yasser Arafat.”
Like Suha Arafat, who calls her husband's death a "political assassination," Kalman believes Arafat was poisoned by polonium.
Kalman says he and his co-author, Matt Rees, "approached the claim with a cynical mindset," but were convinced of the poisoning by details from Palestinian members of an investigative commission that was abruptly disbanded in 2005.
"The polonium has to have been provided to the conspirators in Arafat's close circle by a state player. We don't know who. The fact is that Israel wanted for years to get rid of Arafat, however, it is highly unlikely that Israel would have murdered him at that point," Kalman said.
Israel's foreign ministry spokesman dismissed outright any possibility that Israel had a hand in ending Arafat's life.
"It is impossible to take any of this seriously," an exasperated Yigal Palmor told GlobalPost.
"It is not even pseudo-science. If Arafat had been killed by polonium, the entire area in which he was buried would have been affected. People working there would have been affected. It is a well-known site in the center of Ramallah. The environment in which he had lived would have been contaminated. How is it possible that now we find polonium, but the French hospital in which he died detected none at all?
"This is just a telenovela," he finally said, using the Spanish term for “soap opera.”
Arafat died in a French military hospital outside Paris, to which he had been taken after falling ill at his home in the West Bank. Doctors at the hospital have consistently maintained that Arafat was not affected by radiation poisoning.
Late last year, Dr. Roland Masse, a physician at the hospital, told the Times of Israel that there was “absolutely no way” the Palestinian leader was poisoned.
The symptoms of polonium poisoning would have been “impossible to miss,” he said. Masse emphasized that Arafat had been tested for radiation poisoning before his death. "A lethal level of polonium simply cannot go unnoticed," he added.
Arafat's body was exhumed for testing at his widow's request a year ago.
Asked how polonium would have been found in Arafat's remains, Palmor, the Israeli foreign ministry spokesman, said, "I have no idea. I'm not a scientist or a detective or a conspiracy theorist. One thing we do know is that there are many questions about the chain of evidence."
Author Kalman says Palestinian investigators he spoke with "would like to ask some tough questions of three men in particular: Palestine President Mahmoud Abbas; Tayyeb Abdul Rahim, the secretary general of the president’s office under both Arafat and Abbas; and Muhammad Dahlan, the Gaza security chief who became Abbas’s interior minister."
From Switzerland, Bochud, the scientist, said only that the examination's results "moderately support" the claim of polonium poisoning.
Suha Arafat interpreted the results — and the opinion of the Swiss experts — rather differently.
"When you ask [the Swiss scientists] the question directly, they will tell you, 'Of course it's a murder.' There's no other explanation," she claimed in an interview with ABC News.
Polonium has a half-life of 138 days, meaning four months after death, half the amount of polonium in a sample would be detectable; after a year, only one-eighth. The time elapsed since Arafat's death and what Swiss scientists called the samples' confused "chain of custody" render conclusions highly uncertain.
Patrice Mangin, one of the scientists involved in the Swiss investigation, said Thursday he was sorry an autopsy had not been conducted at the time of Arafat's death, nine years ago.
If it had, what would the conspiracy theorists have claimed instead?