Donald Trump, Israeli forces and the release of Australian academic Kylie Moore-Gilbert have all been linked to the killing of Iran’s top nuclear scientist.
And Iran’s supreme leader, Ayatollah Ali Khamenei, has promised to seek revenge.
So what happened, and why should we be worried?
On Friday, an Iranian scientist called Mohsen Fakhrizadeh – believed to be the brains behind a secret Iranian nuclear weapons program – was ambushed with explosives and machine gun fire in the town of Absard, 70 kilometres east of Tehran.
So far, no one has claimed responsibility for the attack.
However, given Israel is already the key suspect behind a string of attacks on Iranian nuclear figures, fingers are pointing to Jerusalem as the main culprit.
Ahron Shapiro, a senior policy analyst at the Australia Israel and Jewish Affairs Council, said it was in the interests of many groups – not just Israel – to thwart Iran’s nuclear program by killing Mr Fakhrizadeh.
“There’s no question that anybody who wants to act against an Iranian nuclear weapons program would be looking at this particular scientist as somebody who is a real threat,” he said.
“Whoever did it probably did it with the blessing of the United States in one way or another, whether it was implicit or explicit.”
Why the timing is fishy
Less than a week ago, University of Melbourne lecturer Kylie Moore-Gilbert was finally freed from an Iranian prison after nearly two years of incarceration.
Her release occurred at the same time Thai authorities made a deal with Iran to transfer three Iranian men linked to a bomb plot targeting Israeli diplomats back to Tehran.
Tehran said Dr Moore-Gilbert was released in a swap for the jailed Iranians, though Thai officials have declined to call it a swap and Prime Minister Scott Morrison has repeatedly refused to confirm details of any such arrangement.
But the timing is “very interesting”, Mr Shapiro said.
“The trade – the people who had been arrested for terrorist planning in Thailand – these were people who had targeted Israel.”
Was the killing of Mr Fakhrizadeh a warning from Jerusalem?
The last gasps of Donald Trump
Outgoing US President Donald Trump has until January 20 before rival Joe Biden is due to take over the White House.
What he does with his remaining days in office could, in a worst-case scenario, result in a nuclear war.
So was Mr Trump a key player in the Iranian scientist’s assassination?
Earlier this month, Mr Trump asked senior advisers in an Oval Office meeting whether he had options to take action against Iran’s main nuclear site in the coming weeks, The New York Times reported.
However, the Times reported, senior advisers warned against a military strike over fears it could escalate into a broader conflict in the final weeks of his presidency.
Associate Professor Tilman Ruff AM, co-founder of the International Campaign to Abolish Nuclear Weapons (ICAN), said “the last gasps of the Trump administration is a particularly dangerous time for the world”.
“Donald Trump is a very vengeful person,” Dr Ruff told The New Daily.
“He will seek to constrain options for and make a big mess for the new administration.”
He said the assassination could provoke a violent response from hardliners in Iran that may lead to a shooting war with Israel or an escalation of violence across the Middle East.
It will also make it much harder for Mr Biden to revive the 2015 Iranian nuclear deal that Mr Trump abandoned in 2018, Dr Ruff said.
The Iranian nuclear deal
The Joint Comprehensive Plan of Action, known as the Iran nuclear deal, was an agreement reached between Iran and members of the UN Security Council in 2015.
Under the accord, Iran promised to reduce its stockpile of uranium to safe levels that were too low to make a nuclear bomb in exchange for relief from economic sanctions.
And the deal was working, Dr Ruff said.
“Iran accepted safeguard conditions that were more intrusive than any country has ever accepted on its nuclear program in the past, with state-of-the-art surveillance,” he said.
That was until 2018, when the hard-won deal fell apart after Mr Trump suddenly withdrew the US from the agreement and dumped crushing sanctions on Iran.
Since then, Iran has been building more advanced centrifuges that would enable it to produce material for a potential nuclear bomb several times faster.
But if you ask Israeli Prime Minister Benjamin Netanyahu, the deal didn’t go far enough anyway.
“There must be no return to the previous nuclear agreement,” he declared shortly after it became clear Mr Biden – who plans to reinstate the nuclear deal – would be the next president.