In Jewish tradition, the world is said to rest on three fundamentals. Nuclear projects also have three fundamentals: nuclear material, equipment and manpower.

A nuclear weapon requires a sufficient quantity and quality of uranium or plutonium. It also requires enrichment facilities for the material and the means to deliver it to its target (bombs and aircraft, warheads and missiles, and on a tactical level, shells and landmines.) It also needs scientists, engineers and operators. It needs people to push the button, and it needs people to build whatever goes flying when that button, or switch, is triggered.

Even the most fervent Shi'ite Muslims, who believe in Allah and his three prophets, will have a hard time believing that mere happenstance is causing people in Iran's nuclear industry to blow up. And it's precisely these people and no one else who about every two months are meeting their deaths.

Human involvement is the target of the Iranians' suspicions, and when it comes to every explosive charge delivered on the back of a motorcycle, as if it were a pizza being delivered, the Iranians finger one culprit: Israel. And that's not because reputed Israeli mobster Yaakov Alperon met his fate in a similar manner on a Tel Aviv street.

Comments on Tuesday by IDF Chief of Staff Benny Gantz about unnatural occurrences in Iran would tend to reinforce conjecture about some kind of plot. But in practice it doesn't matter if this suspicion is correct, half correct or even less than that. It doesn't matter whether the assassinations are Made in Israel or the work of unknown assailants who simply share a common enemy with Israel in the form of a fanatic Islamic regime in Tehran.

The ambiguity is the sibling of the ambiguity surrounding Israel's alleged nuclear capability. It serves the following purpose: the working assumption that Israel knows who is active in Iran's nuclear project, knows where and when to find them and how to eliminate them from the community of scientists. In other words, every Iranian nuclear scientist will know he's in the crosshairs.

Infiltrating into the heart of the Iranian capital or outlying towns, or remote highways near security installations; assassinations; departures from this world without leaving evidence of who carried out the act - all this reflects a systematic approach and professionalism. True, these qualities didn't characterize the assassination of Mahmoud al-Mabhouh two years ago, which the Dubai police attributed to the Mossad, but two years earlier there was a much more successful assassination operation in Damascus against Imad Mughniyeh, so the balance of suspicions remains intact.

The West's campaign, under American leadership, against the Iranian nuclear program is not a war of choice. In its absence, tensions in the Middle East would intensify to an intolerable level. If we are to judge by the thunderous results, it's a very selective war with carefully selected targets. The targets are not symbols of the regime or even theological, diplomatic or military decision-makers.

Not that they have immunity. It could be that they are well-protected, but it appears that no extraordinary effort has been invested in them either. The reason for this could be the survival instinct of ministers and military commanders in Western capitals who fear Iranian retaliation for the assassination of senior figures. This would be more sophisticated than the intelligence-gathering before the assassination plot on the Saudi ambassador in Washington, an amateurish case that was uncovered via intelligence from informants. But it also involves judgment over limiting the campaign's scope.

Limiting the assassinations to nuclear scientists conveys a double message to Iran. First, whoever is sending the assassins will not be reconciled to a militarily nuclear Iran. They are determined to damage the nuclear program in all its aspects. Whoever is sending the assassins also understands that any system that is damaged or even destroyed can be rehabilitated if the right people are found to revive it.

These people, some of whom are being blown up, would certainly feature in the West's target bank after an attack on Iran's nuclear facilities, if one is carried out, to head off efforts to restore the program. The West would do this to impede the rebuilding of what would remain in ruins for years.

Second, this is not a wide assault on the Iranian regime, just on its nuclear arm. Iran's leaders must decide now on a small scale and all the more so after an attack whether to respond to a precision strike by opening a wider war.

If the West were to attack Iran along an entire front, the response would have to be major. On the other hand, an attack on the nuclear facilities alone would leave many assets in Iran's hands that it would be hesitant to lose in a tit-for-tat response. These include oil installations, Revolutionary Guard bases and above all the regime itself and its leaders.

Therefore, in his death on Wednesday, Mostafa Ahmadi Roshan directed his leaders to do some soul-searching. The cyclists carrying the explosives really were messengers. In addition to delivering the sentence on the nuclear scientist, they were sending a message to the authorities in Tehran.

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