Barber Mohammed Hamad was in no doubt about the reasons for Yasser Arafat's death just under eight years ago. As he trimmed a customer's hair in his shop in the Amari refugee camp yesterday, he welcomed the news that French prosecutors have opened a murder investigation. And he insisted that "99.9 per cent of people" in the city where the previous Palestinian President was confined in his sandbagged headquarters for the final two years of his life "believe Abu Ammar" – he uses Arafat's nom de guerre – "was murdered, poisoned".

While strongly suspecting that the actual deed was perpetrated by a Palestinian with regular access to Arafat, Mr Hamad, 44, was equally certain that Israel and its then Prime Minister Ariel Sharon were behind it. "Arafat refused at Camp David [in 2000] to sign a peace agreement which left [Jerusalem's] al-Aqsa [mosque] under the control of Israel. Sharon wants to control Jerusalem, East and West. He wants to get rid of Abu Ammar. He accused him of starting the intifada and controlling the al-Aqsa Martyrs' Brigades."

Just one barber's view, of course. But what is disconcerting for all those who regard the accusation that Israel covertly assassinated Arafat as belonging on the wilder shores of conspiracy theory is how widely it is shared among level-headed Palestinians, from the West Bank streets to some of the upper reaches of their leadership.

Qaddoura Fares, the respected senior Fatah official now responsible for the welfare of the 4,500 Palestinian prisoners in Israeli prisons, is a long-time advocate of peace negotiations on a two-state solution.

Yet, he too appears convinced, in the face of repeated denials by Israel, that a President he knew well was murdered on the orders of a Prime Minister who had a personal history of enmity with him going back more than 20 years, and who persistently depicted him as an "obstacle to peace".

Sharon, he says, understood well that Arafat was a uniquely unifying leader for the Palestinians and as a "militant leader" himself "the Israeli PM knew that the [second] intifada would not have happened without a green light from [Arafat]".

Now that the suspicion that he was poisoned has been revived by the identification of traces of deadly polonium on the clothes handed to investigators from the Al Jazeera TV channel by Arafat's widow, Suha, Mr Fares says the Israeli authorities had every reason to ensure that he died as if from natural causes.

"They didn't want him to die as a symbol. They didn't want to make him a martyr. They could easily have shot him if they wanted to."

Around the time in September 2003 when, in the aftermath of a double suicide bombing on a single day, Israel's cabinet took a non-specific, and apparently unfulfilled decision to "remove" Arafat from his Muqata compound in Ramallah, Mr Fares thinks Israel considered a number of options: continued isolation, deportation, arrest and arraignment before a military court – and assassination.

Dismissive of the Palestinian Authority's ability to investigate the death itself, Mr Fares says that the French investigation certainly looks more "credible" and that it will at least ensure that "the issue will be alive, and that it will go on chasing the Israelis".

Still in the coma triggered by the massive stroke which felled him in early 2006, Mr Sharon cannot answer the charges himself.

But while acknowledging Arafat's status as "one of Israel's worst enemies", Mr Sharon's closest lieutenant and former bureau chief Dov Weisglass rebutted them in some detail on Army Radio yesterday.

"We did not physically hurt him when Arafat was in his prime... so all the more so we had no interest in this kind of activity when he was politically sidelined," he said.

Mr Weisglass described having dinner with Javier Solana when the-then EU foreign policy chief took a call from Ahmed Qureia, the Palestinian Prime Minister, asking if Israel would allow the ailing President to be transferred to a Ramallah hospital, Mr Weisglass called Mr Sharon who immediately granted the request. He did the same following day when Mr Solana told Mr Weisglass that Palestinian doctors now said Arafat was very ill and needed treatment in Europe.

And Raanan Gissin, Mr Sharon's long-standing spokesman told the Associated Press that, as the intifada continued, Israeli officials repeatedly raised the option of assassinating Arafat but Sharon always rejected it. Israel "never touched a hair on his head," he said. "The idea was not to kill Arafat, but to change the Palestinian leadership."

But this is anyway not just about Israel. Even many Palestinians believe that if it is ever established that Arafat was assassinated, the truth could make uncomfortable reading in sections of the Palestinian leadership, given that inside help would almost certainly have been needed to reach a heavily guarded President whose food was always prudently shared with others.

Mr Fares, for his part, is certainly not attributing blame to anyone while soberly accepting that any inquiry would have to consider – among much else – the possibility that a Palestinian or Palestinians might have been involved.

Saying that all Palestinians need to give the French prosecutors whatever help they request, he points out the incriminating consequences of not doing so.

"If I am asked to go to Paris and be questioned, and I refuse, then I might as well kill myself," he says. Mr Fares's hope is that the French investigation will somehow begin to find real answers to the questions still swirling here about Arafat's final, fatal illness.

"Ninety per cent of Palestinians believe he was murdered, and 10 per cent that he died of natural causes," he says. "Even if the 10 per cent are right, we need to get to the truth."

Q&A: Polonium

Q. What is it?

Discovered by Marie Curie in the 19th century, polonium is a highly radioactive element, rarely found outside the military and scientific establishment. The particular isotope detected on Yasser Arafat's personal belongings – polonium 210 – occurs naturally in small concentrations in the environment. But high doses of the radioactive substance, which emits radiation in the form of alpha particles, can damage tissues and organs. These cannot pass through the skin, and to pose a danger polonium must be taken into the body, for example by eating it or breathing its radiation.

Q. Has it been used to poison people before?

Polonium hit the headlines in 2006, when it was used to kill the former Russian spy turned Kremlin critic Alexander Litvinenko. He died in November that year after falling suddenly ill in London. Subsequent tests found traces of radiation at various locations in London, and eventually linked Litvinenko's death to the presence of a large dose of polonium 210 in his body.

Q. How was Yasser Arafat linked to polonium?

Samples of clothes worn by the late Palestinian leader shortly before he fell ill were sent to a Swiss laboratory this year by the Al Jazeera television network, in co-operation with his widow and daughter. Scientists at the lab in Lausanne went on to discover significant traces of the radioactive element on his belongings.