LONDON - I watched Yasir Arafat´s final homecoming to Ramallah in November 2004 from Bassam Abu Sharif´s roof.

Mr. Abu Sharif, the Palestinian leader´s long-time political adviser, was too overcome with grief at the time to discuss his theories about his hero´s death. "I still can´t believe it," he told me on that day. "The world without Arafat is a different place."

It was not long, however, before Mr. Abu Sharif emerged as a prominent spokesman for what rapidly became a near-universal consensus among Palestinians that their leader had been murdered.

That theory may finally be laid to rest - or maybe not - after the Palestinian Authority decided, in principle, to exhume Mr. Arafat´s remains, possibly within days, following a claim that he might have been poisoned with polonium, a radioactive element.

The suggestion was raised in a report this week by Al Jazeera that cited findings by doctors at the University of Lausanne´s Institute of Radiation Physics.

They were said to have identified unusually high levels of polonium 210 in personal items belonging to Mr. Arafat and provided by his widow, Suha.

As my colleague Isabel Kerschner wrote from Jerusalem, the report caused an uproar in the Palestinian territories, "rekindling unresolved questions about the death and theories that he had been killed by agents of Israel or by Palestinian rivals."

The polonium theory appears to be at odds with an earlier claim by Mr. Abu Sharif that Mr. Arafat was poisoned with thallium, a colorless, tasteless odorless compound.

The former adviser wrote in a 2009 book that he had suspected poisoning even during Mr. Arafat´s 2004 illness. The two men had been close. Mr. Abu Sharif, once involved in a notorious airline hijacking and later disfigured by a Mossad bomb in 1972, became an architect of the Palestinian leader´s strategy in the late 1980s to open negotiations with Israel.

"I was positive they were poisoning his food on a daily basis and doing it right under our very eyes," he wrote in Arafat and the Dream of Palestine.

Early last year, he put forward his thallium claim, basing it on tests carried out by "the most prominent forensic toxicology expert in the U.K.," whom he did not name.

(For the benefit of conspiracy theorists and others, thallium was the favored poison of Saddam Hussein´s assassins, while polonium - hard to obtain without access to nuclear technology - was linked to the 2006 death of Alexander V. Litvinenko, a former K.G.B. agent and critic of the Russian government.)

Israel´s Jerusalem Post came up with its own conspiracy theory this week, claiming Mr. Abu Sharif´s contributions to the poisoning debate were part of an attempt to pin blame on Israel and divert any possible link to Mahmoud Abbas, Mr. Arafat´s successor as president of the Palestinian Authority.

An Al Jazeera report in 2009 quoted Farouk Qaddumi, a senior exiled Fatah dissident, accusing Mr. Abbas of having conspired with Israel to kill Mr. Arafat. The broadcast led to a ban on Al Jazeera in the Palestinian territories.

"To cleanse himself and counter the politically loaded charges, Abbas recruited Bassam Abu Sharif, Arafat´s consigliore, nicknamed the ´Face of Terror´," The Jerusalem Post wrote in an editorial on Wednesday. "But Abu Sharif´s tack was hardly to deny the calumny. He merely modified it to place the culpability more squarely on Israel."

None of which proves, of course, that Mr. Arafat was not poisoned.

One thing is for certain. Even if the exhumation goes ahead and the autopsy comes up clean, many Palestinians, including no doubt Bassam Abu Sharif, will refuse to accept that the leader of the Palestinian revolution passed away without someone´s helping hand. (Copyright 2012 The New York Times Company 07/06/12)