It started with the strange death of Muhyideen al-Sharif. The mutilated body of the Hamas bomb-maker - high on Israel's wanted list - was found two weeks ago after an explosion in a Hamas arsenal in Ramallah, north of Jerusalem.
It soon emerged he had been murdered and the bomb was part of an unsuccessful cover-up.
Hamas claims Sharif died at the hands of Israeli agents, possibly working with Palestinian security. The Palestinian Authority says he died at the hands of Imad Awadallah, another Hamas leader, in a row over $800,000 (pounds 500,000) transferred to the Izzedin al-Qassem brigades, the military wing of Hamas. It says it has the 9mm pistol used to kill him and has discovered the apartment where he died. It even has an alleged signed confession by a participant.
Mr Arafat is eager to prove it was Hamas, not Israel, which killed Sharif because he does not want to see his strategy of trying to woo the US and the Europeans ruined by another Hamas suicide-bombing campaign. This would give Benjamin Netanyahu, the Israeli Prime Minister, the excuse to suspend talks on partial Israeli withdrawal from the West Bank.
For this reason he has arrested 60 Hamas activists, though Hamas say the real figure is 300. Palestinian journalists who have interviewed Hamas members have been called in for questioning. It is the most serious confrontation between the Palestinian Authority and Hamas, the only effective Palestinian opposition, since Mr Arafat's police opened fire on an Islamic demonstration in Gaza in 1994, killing a dozen people.
Mr Arafat is probably denting Hamas as an organisation. But the expertise, equipment and personnel needed for a suicide-bomb attack are limited. No doubt secret Hamas cells still exist in the West Bank which could carry one out. But the Palestinian leader also wants to convince the Palestinian public, who must bear the brunt of Israeli retaliation in the event of an attack, that Sharif died in an internal wrangle. There is strong but not overwhelming evidence for this. The Palestinian Authority relies for its circumstantial story on Ghassan Adassi, who signed a statement describing what happened. But the Hamas internet carries a letter from Mr Adassi saying his confession was extracted by torture.
"They beat me harshly and prevented me for sleeping for three continuous days," writes Mr Adassi. "They hung me by my hands from the ceiling of my cell. They compelled me to sign by force." This is all too likely to be true, since Palestinian Preventive Security routinely uses torture.
Conversely, the fact that Mr Adassi was tortured and his confession is untrue does not mean the details of how Sharif died, as revealed by the official investigation, are not true. In the apartment discovered in Ramallah the investigators say they have discovered traces of the explosives used to blow him up. They have also found fragments of food similar to that found in his stomach during the autopsy.
Jibril Rajoub, head of Preventive Security, denies Mr Adassi was mistreated, saying: "If he was strong enough to type this letter, I don't see how he was tortured."