Earlier this summer, when there was still some semblance of co-operation between the Israeli and Palestinian security forces, their combined efforts led to the discovery of a Hamas bomb factory just outside Jerusalem. But any joy at that success was tempered by the suspicion that, from the layout of the explosive material found at the scene, the factory had already been used to prepare six bombs.
Since then, five Hamas suicide bombers have struck in Jerusalem - two at a vegetable market in July, three more on the Ben-Yehudah mall three weeks ago. Now, with the investigation into those bombings finally making progress, Israeli security officials fear that they are racing against time; that the sixth bomb is still out there, in the hands of a suicide bomber who may strike at any moment.
It was the Israeli Prime Minister, Mr Benjamin Netanyahu, who announced, on Tuesday, that Israel had traced four of the five recent suicide bombers, and that they had come from the West Bank village of Assira, near Nablus.
Opposition politicians and some security officials are now castigating him for speaking out prematurely. Their concern is that, if a sixth bomber is on the loose, headlined reports of the net tightening around his network of Hamas militants may leave him with the feeling that he is about to be captured, and that he might as well carry out his bombing right away.
The Palestinian President, Mr Yasser Arafat, yesterday rejected Mr Netanyahu's assertions that he was to blame for the bombings, noting that since Assira remains under overall Israeli security control, "it is not our responsibility."
However, he did acknowledge that the four bombers had run away from a Palestinian jail in Nablus last year, a facility with open cell doors, and daily unsupervised free time in town. It was from one such day trip last September that the quartet apparently simply failed to return.
Mr Arafat yesterday ordered a tightening of security at the jail, and the arrests of 20 suspected Hamas militants inside Nablus. His security chiefs also met on Tuesday night with their Israeli counterparts, who handed them a list of dozens more alleged militants.
David Horovitz is managing editor of the Jerusalem Report