Mossad "obviously has had resources on the ground in Iran for years", a former intelligence operative with links to the Israeli spy agency told the ABC, speaking on condition of anonymity.
And another specialist on irregular warfare, Doug Livermore, said the operation's "footprint would be small by design but elite: likely a joint team of special operations units, cyber operators and intelligence planners".
The intelligence agency was the tip of the spear in Israel's Operation Rising Lion, an opportunistic strike on its most formidable adversary, Iran, that triggered the so-called "12-day war".
Launched at 3am on June 13, Israel targeted locations across Iran, including nuclear facilities, missile sites and military bases. Several of Iran's top officials and nuclear scientists were killed in the air strikes.
Iran fired back.
On Sunday, the US dropped "bunker bombs" on Iran's three nuclear facilities at Fordow, Natanz and Isfahan.
The top US military commander said Tehran put up no resistance.
"Iran's fighters did not fly, and it appears that Iran's surface-to-air missile systems did not see us," General Dan Caine said.
US Defense Secretary Pete Hegseth paid tribute to Israel's "incredible military success … in degrading Iranian capabilities, degrading Iranian launchers, MRBMs [medium-range ballistic missiles]".
Last week, Mossad released footage purporting to show how it laid the groundwork for air strikes right under the regime's nose.
Videos depicted its agents at work sabotaging air defences inside the Islamic Republic, deploying a mobile weapons system, and a drone's-eye view of their targets.
Mossad also pinpointed the whereabouts of top Iranian military commanders and nuclear scientists in a simultaneous array of assassinations that served as a chilling warning to Tehran's elite.
The Israel Defense Forces (IDF) said the June 13 operation was a pre-emptive strike against an Iran that was "closer than ever to obtaining a nuclear weapon … an existential threat to the state of Israel and a significant threat to the wider world".
Israel refuses to confirm or deny it has nuclear weapons but the Stockholm International Peace Research Institute says it is the only Middle Eastern nation that does.
The IDF said it was also responding to "ongoing aggression" from Iran, including missile attacks last year after Israel bombed its Syrian embassy.
But a United Nations-appointed expert argues Israel's actions broke the laws of war.
Operation Rising Lion also put Mossad at the centre of an operation that some of its own former chiefs once thought too dangerous to contemplate.
'Crime organisation with a licence'
Mossad has been described by one of its former heads, Tamir Pardo — a fierce critic of the Benjamin Netanyahu government — as "a crime organisation with a licence".
Its notoriety stems from decades of operations, from its capture of Nazi war criminal Adolf Eichmann in Argentina to the presumed assassination of Iran's premier nuclear scientist using a remote-controlled machine gun.
A decade earlier, it was from within Mossad that Israeli Prime Minister Benjamin Netanyahu met unexpected opposition to his push for an assault on Iran over its nuclear program.
That included the then-head of Mossad, Meir Dagan, who the prime minister had lauded as having "a rocket-propelled grenade between his teeth".
Dagan later told the New Yorker that "an Israeli bombing would lead to a regional war … galvanise Iranian society behind the leadership and … justify Iran in rebuilding its nuclear project and saying, 'Look, see, we were attacked by the Zionist enemy and we clearly need to have it.'"
This year, a window of opportunity opened for Mr Netanyahu in the form of a finding by the United Nations nuclear watchdog.
On June 12, the International Atomic Energy Agency declared Iran in breach of non-proliferation obligations for the first time in 20 years.
Director-general Rafael Mariano Grossi said the agency had witnessed "rapid accumulation of highly enriched uranium".
Iran, which, unlike Israel, is a signatory to the Nuclear Non-Proliferation Treaty, .
Mr Netanyahu ordered a strike on Iran the next day.
This time, Mossad was on the same page.
An 'unbelievable' operation
The agency had been stung by Israel's costliest intelligence failures leading up to the October 7 attacks by militant group Hamas in 2023.
Hamas killed almost 1,200 people, mostly Israeli civilians, including 36 children, and took about 250 hostages to Gaza, according to Israeli officials.
Israel's subsequent strikes on Gaza have killed more than 56,000 people, including 17,121 children, according to the Gaza Health Ministry.
The former intelligence operative with links to Mossad, speaking to the ABC on condition of anonymity, said Israeli intelligence officers were "aghast" at their part in the failures.
"They did have information related to planning for the attacks but this was dismissed," the source said.
The source said that "Hamas and Iran realised they might be technically compromised" and planted misinformation that threw Israel's vaunted spooks.
"It was later determined that there was an over-reliance on technical intelligence gathering rather than traditional human source methods," the source said.
Israeli intelligence agencies had since "doubled down" on its spy programs, they said.
This has proven less challenging inside Iran, where civil society chafes against a repressive theocratic regime.
Mossad "obviously has had resources on the ground in Iran for years", which probably involved a mix of both Israeli and foreign operatives, the former intelligence source said.
Mossad commando units working covertly inside Iran smuggled in drones and missile systems, which were in place before the assault.
They targeted and destroyed parts of Iran's air defence infrastructure and surface-to-surface missile launchers.
Mr Livermore, who works with the Irregular Warfare Initiative in the US, said the operation at its heart was a tactical success for Israel.
"A strike of this magnitude would have required years of intelligence preparation — human intelligence, signal intelligence and imagery intelligence — all fused into a real-time operational picture," he said.
"The manpower footprint would be small by design but elite: likely a joint team of special operations units, cyber operators, and intelligence planners.
"Extensive rehearsal, denial and deception measures, and inter-agency coordination would be essential."
With the Islamic Republic's air defences hobbled, hundreds of Israeli jets took over the sky, unloading bombs at will on Iran's military and nuclear installations — and the soldiers and scientists who oversaw them.
Ran Porat, a researcher at Monash University's Australian Centre for Jewish Civilisation, said it was an "unbelievable" operation that highlighted the precision of Israeli intelligence.
"The pinpoint intelligence — that is the deep penetration of the Israeli intelligence community to be able to know where all the Iranian top echelon [figures] or the top brass are meeting and taking them out in complete surprise," he said.
The assassinations sparked alarm among Tehran's elite, and a sudden ban on government and security officials using communication devices, according to the state-linked Fars News Agency.
Iranian MP Hamid Rasaee posted on X that Israel's surveillance via mobile phones had become "the enemy's … tool for assassination".
"The most important decision at this point is: All mobile phones of military commanders, influential officials, and nuclear scientists (including themselves, their families, companions, and those around them) should be collected," he said.
Mr Livermore predicted the Israeli strike would have a psychological impact on Iran's leadership.
"It reinforces to Iranian elites that Israel can reach deep into their most secure infrastructure," he said.
"Over time, this could fuel paranoia, internal distrust, and perhaps spark further instability, especially if repeated or accompanied by economic and political pressure."
Days after the attacks, Iranian authorities executed Esmail Fekri, who had been found guilty of spying for Israel in what Amnesty International described as a "grossly unfair trial".
The human rights organisation said another eight people faced the death penalty under Tehran's "misguided attempt to project strength" in war with Israel.
Three people were put to death on Wednesday in Iran, accused of spying for Mossad.
State-aligned news agencies said the people had brought "assassination equipment" into the country disguised as shipments of alcohol, which was supposedly used in the assassination of one of their public figures.
About 700 people have reportedly been arrested over the last 12 days, accused of being Israeli mercenaries.
'What the West wants'
Dr Porat said the international community's failure through diplomacy to prevent North Korea from developing nuclear weapons should serve as a warning.
"The lesson is we should always aspire for peace, but with extremists, the conversation is, sadly, through the barrel of a gun," he said.
"We can never, ever allow non-democratic states to have nuclear weapons."
Israel has argued it has the right to pre-emptive action to safeguard the state's survival in the face of Iranian threats.
But international lawyer Ben Saul, who is the United Nations Special Rapporteur on the Promotion and Protection of Human Rights and Fundamental Freedoms while Countering Terrorism, said Israel's attacks broke the laws of war.
"Every death, whether it's a part of the military, whether it's a nuclear scientist, whether it's a completely uninvolved civilian, all of that is illegal," Dr Saul said.
"Under international law, you can only use military force if it's in self-defence because you've been attacked.
"Iran doesn't have a nuclear bomb and it hasn't attacked Israel with one, so it's nowhere near the ballpark of what would give Israel a right to self-defence."
Dr Saul said the US-led invasion of Iraq in 2003 on unproven claims of weapons of mass destruction showed the West had been willing to pursue "what the West wants in security terms, even if that rides roughshod over international law".
"The law is one thing, and then politics is a whole other ball game," he said.
"It's disappointing but it erodes legitimacy and compliance with international law by everybody."
