Explosions and gunfire in the streets of Tehran early on Monday killed a senior Iranian nuclear physicist and badly injured one of his colleagues, but left an eerie silence in which the killers are yet to claim responsibility for the daring, breakfast-time attacks.
Accounts are sketchy - shortly before 8am; assassins on motorcycles; magnetised bombs slapped to the side of the victims' vehicles as they left for work; and a Peugeot 206 - the police gave chase and fired shots, but in rush-hour traffic they lost what they thought was a get-away car for some in the hit team.
Coupled with earlier mysterious deaths, offers of million-dollar foreign inducements for nuclear secrets, and the unleashing in Iran of a worm that can devour computer systems, it seems that a sophisticated covert effort, or efforts, is under way to thwart Iran's nuclear ambitions - quite apart from all the high-brow, over-the-radar stuff we read from the United Nations and other international forums.
Clearly, someone is attempting to eliminate Iran's best scientific brains. But coinciding with the WikiLeaks dumping of 250,000 confidential dispatches by American diplomats into the public domain on Sunday, a good number of which reveal intense ill will towards Iran in the Middle East, the range of suspects for the near-identical attacks on Monday is a new measure of Tehran's isolation in the world.
The President, Mahmoud Ahmadinejad, was quick to blame ''Western governments and the Zionist regime'' for the attacks.
He could be right. The US and Israel run covert programs aimed at halting Tehran's nuclear program and in Israel the well-regarded intelligence analyst Yossi Melman wrote in Haaretz of Ahmadinejad's jab at Israel: "Most experts who follow Middle East politics and Mossad history would agree."
The US president George W. Bush authorised a covert operation to sabotage Iran's nuclear effort. Israel also has form - and success - in eliminating figures in enemy organisations within and beyond its borders.
But there are local suspects, too.
First, there is the Sunni Jundullah movement, which claims to have killed hundreds of Iranian security personnel and civilians in its fight for the rights of Iran's Sunni minority. On the day of the attacks, Jundullah released a video of a hostage they say worked at a secret nuclear facility - his name was given as Amir Hossein Shriani and in the video he claimed to be aware of a weapons program. But the video made no reference to Monday's bombings.
Next is the People's Mujahideen of Iran. But this is a group that claims to have renounced its armed struggle - fought first against the deposed Shah of Iran and then against the Islamic revolution of Ayatollah Ruhollah Khomeini.
Lastly, and more intriguingly, is speculation that the attacks might have been the work of the Iranian authorities. Rather than sweep them under the carpet, the regime has made show trials of nuclear staffers accused of being entrapped by foreign agents offering to buy information on the nuclear program.
The rationale behind speculation that Iran had turned on its own is that the targets might have been lured into planning to defect as a result of their interaction with international colleagues in a UN-sponsored program in Jordan.
A second argument in this line of speculation is that the government mounted the attacks to spread fear among its domestic opponents.
On balance, however, the most likely perpetrators or sponsors of those who mounted the attacks are to be found outside Iran - probably in Israel or in the US.
The man killed on Monday was Majid Shahriari who, according to the chief of the Iranian Atomic Energy Organisation, Ali Akbar Salehi, ran a large project for the organisation.
Like his injured colleague Fereidoun Abbasi, 52, Shahriari was a faculty member at Shahid Beheshti University in Tehran. The wives of both men were injured in the attacks.
Salehi - who had once taught Shahriari - was in tears on state TV on Monday evening. "They are mistaken if they think they can shake us,'' he said.
Feted by Ahmadinejad in 2007 as ''academic of the year'' and a member of the Islamic Revolutionary Guards, Abbasi is cited in UN Security Council resolution 1747 for his involvement in nuclear or ballistic missile activities and as a close colleague of Mohsen Fakhrizadeh-Mahabadi who, according to Western intelligence agencies, runs Iran's nuclear weapons program.
In January, their colleague Masoud Ali Mohammadi, an expert on particle physics, died when a bomb strapped to a motorcycle which had been parked outside his home was detonated remotely as he left for work. And in 2007, Iranian television reported the death of the nuclear scientist Ardeshir Hosseinpour from ''gas poisoning''.
After Monday's attacks, Ahmadinejad surprised many observers by making what appeared to be the first high-level admission that the Stuxnet computer worm, which is often reported to be part of an Israeli covert operation, had caused difficulties for the thousands of centrifuges in which Iran enriches uranium.
Refusing to address Stuxnet specifically, Ahmadinejad, as reported by Reuters, said: "They succeeded in creating problems for a limited number of our centrifuges with the software they had installed in electronic parts. They did a bad thing [but] fortunately our experts discovered that and today they are not able [to do it] any more."
Earlier this year, Stuxnet was reportedly detected around the world - but most notably in computers at Iranian nuclear facilities.
Days before Ahmadinejad's admission, a report by the International Atomic Energy Agency revealed that almost 5000 centrifuges at the Natanz uranium-enrichment plant had come to a halt in mid-November after a steady decline over a period of months, for reasons that were not divulged.
Previously Iran had revealed that the computer virus, which disrupts the centrifuges by prompting them to spin uncontrollably, had been detected in the personal computers of staff at its Bushehr nuclear power plant - but it had insisted that systems connected to its nuclear program had not been infected.
In July, one of the more bizarre post-Cold War defections came to an end when the Iranian nuclear scientist Shahram Amiri stunned his American intelligence hosts by telling them he wanted to go home to Iran - and that they could keep $US5 million ($5.1 million) they had agreed to pay for Iran's nuclear secrets.
Who to believe? Tehran claimed that American agents had abducted Amiri in May 2009 while he was on a pilgrimage to holy Muslim sites in Saudi Arabia. Washington insisted that Amiri was a willing defector who changed his mind and had opted to return home … after he had spilled the beans.
In tit-for-tat claims, Tehran insisted Amiri had brought back good information on the CIA after spending more than a year with his American handlers. And the CIA said thank you very much for all the useful data on Iran's nuclear program.
Angst over Iran's nuclear program - in the US, Europe and Israel, and in much of the Arab world - is driven by a widely held belief that its uranium enrichment effort is geared to producing weapons, and not to a nuclear electrical generation network, as claimed by Tehran.
The WikiLeaks papers are a stark revelation of the hideous complexities of the global campaign to rein in Tehran's nuclear drive before it imposes a new balance of power on the Middle East - between a nuclear-armed Iran, which as a Shiite Persian state would be lording it over its Sunni Arab neighbours, and a nuclear-armed Israel, which desperately wants to maintain its monopoly as the region's only nuclear power.
In the middle of it all sits Washington, under intense pressure from Israel to attack the disparate nerve centres of Iran's nuclear program - or see Israel do the job itself.
In mid-2009, according to the leaked dispatches, the Israeli Defence Minister, Ehud Barak, figured there was a six- to 18-month window in which it might be possible to stop Iran going nuclear and after that, he said, "any military solution would result in unacceptable collateral damage".
The dispatches reveal a strong unanimity of view between Israel and its Sunni Arab neighbours who, ordinarily, have little to say in public about Iran. But in the privacy of diplomatic tete-a-tetes with the Americans, the leaders or senior officials of Saudi Arabia, Egypt, Jordan, the United Arab Emirates and Bahrain have urged the US to strike their next-door neighbour.
This Arab message was the surprise element in the leaked documents. As The New York Times said of the Israeli position: "There was little surprising in Mr Barak's implicit threat that Israel might attack … As a pressure tactic, Israeli officials have been setting such deadlines, and extending them, for years."
Both sides, Israeli and Arab, pile on lectures for their US visitors.
The Israeli military intelligence chief, Major-General Amos Yadlin, insisted last year: "Israel is not in a position to underestimate Iran and be surprised like the US was on September 11, 2001."
And Saudi Arabia's King Abdullah still smarts at what he claims was the last time Washington refused to heed his advice - when it opted to invade Iraq in 2003. "US policy [has] now given Iraq to Iran as a gift on a golden platter," the dispatches quote the king.
The US Defence Secretary, Robert Gates, does not dispute the thrust of what comes out of the region, but he doubts that attacking Iran would be a significant setback for Tehran's nuclear program. "We risk nuclear proliferation in the Middle East, war prompted by an Israeli strike, or both," he said.
King Abdullah confirms Gates's belief on proliferation. "[If Iran gets nuclear weapons] everyone in the region will do the same - including Saudi Arabia."
But in February, when Gates had lunch with the French Defence Minister, Herve Morin, the US Defence Secretary saw little value in attacking Iran. "[Any strike] would only delay Iranian [nuclear] plans by one to three years, while unifying the Iranian people to be forever embittered against the attacker."
There spoke a man who only too well understood the cost and fall-out of having to fight two hugely expensive wars of invasion, occupation and insurgency in Iraq - Iran's western neighbour; and in Afghanistan - Iran's eastern neighbour.
But any hope that the WikiLeaks dump had cleared the fog that often blankets the Iranian nuclear program was dashed on Wednesday, when The Washington Post poured a big bucket of cold water on alarming media reports - based on the diplomatic dispatches - that claimed North Korea had supplied Tehran with 19 Musudan BM-25 missiles which, if true, would extend Tehran's target range deep into Western Europe and Russia.
Not likely, said the experts who spoke to the Post. While some speculated that the Musudan, based on a Soviet design and unveiled during an October 10 military parade to mark the 65th anniversary of North Korea as a one-party state, was a mock-up, a senior American intelligence officer said "the sale of such an actual missile does not fully check out".
