Palestinian militant Mohammed Deif began planning the operation that has killed more than 1,200 people in Israel

It was in May 2021, after a raid on Islam's third holiest site that enraged the Arab and Muslim world, when Palestinian militant Mohammed Deif began planning the operation that has killed more than 1,200 people in Israel, according to a source close to Hamas in Gaza.

Israel calls last week's devastating attack by Hamas its 9/11 moment. The secretive mastermind behind the assault, Palestinian militant Mohammed Deif, calls it Al Aqsa Flood.

The phrase Israel's most wanted man used in an audio tape broadcast as Hamas fired thousands of rockets out of the Gaza strip on Saturday signalled the attack was payback for Israeli raids at Jerusalem's Al Aqsa mosque.

It was in May 2021, after a raid on Islam's third holiest site that enraged the Arab and Muslim world, when Deif began planning the operation that has killed more than 1,200 people in Israel, according to a source close to Hamas in Gaza.

"It was triggered by scenes and footage of Israel storming Al Aqsa mosque during Ramadan, beating worshippers, attacking them, dragging elderly and young men out of the mosque," the source said. "All this fuelled and ignited the anger."

That storming of the mosque compound, long a flashpoint for violence over matters of sovereignty and religion in Jerusalem, helped set off 11 days of fighting between Israel and Hamas.

More than two years on, Saturday's assault, the worst breach in Israeli defences since the 1973 Arab-Israeli conflict, pushed Israel to declare war and launch retaliatory strikes on Gaza that had killed more than 800 people by Tuesday.

A survivor of seven Israeli assassination attempts, the most recent in 2021, Deif rarely speaks and never appears in public. So when Hamas's TV channel announced he was about to speak on Saturday, Palestinians knew something significant was afoot.

"Today the rage of Al Aqsa, the rage of our people and nation, is exploding. Our mujahedeen (fighters), today is your day to make this criminal understand that his time has ended," Deif said in the recording.

There are only three images of Deif: one in his 20s, another of him masked, and an image of his shadow, which was used when the audio tape was broadcast.

The whereabouts of Deif are unknown, though he is most likely in Gaza in the maze of tunnels under the enclave. An Israeli security source said Deif was directly involved in the planning and operational aspects of the attack.

Two Brains, One Mastermind

The source close to Hamas said the decision to prepare the attack was taken jointly by Deif, who commands Hamas's Al Qassam Brigades, along with Yehya Sinwar, the leader of Hamas in Gaza, but it was clear who was the architect.

"There are two brains, but there is one mastermind," the source said, adding that information about the operation was known only to a handful of Hamas leaders.

Secrecy was such that Iran, Israel's sworn foe and an important source of finance, training and weaponry for Hamas, knew only in general terms that the movement was planning a major operation and did not know the timing or the details, according to a regional source familiar with the group's thinking.

The source said that while Tehran was aware a major operation was being prepared, it was not discussed in any joint operation rooms involving Hamas, the Palestinian leadership, Iranian-backed Lebanese militants Hezbollah, and Iran.

"It was a very tight circle," the source said.

Iran's top authority Ayatollah Ali Khamenei said on Tuesday Tehran was not involved in the attack on Israel. Washington has said while Tehran was complicit, it had no intelligence or evidence that points to Iran's direct participation in the attacks.

The plan as conceived by Deif involved a prolonged effort at deception. Israel was led to believe that Hamas, an ally of Israel's sworn foe Iran, was not interested in launching a conflict and was focusing instead on economic development in Gaza, where the movement is the governing power.

But while Israel began providing economic incentives to Gazan workers, the group's fighters were being trained and drilled, often in plain sight of the Israeli military, a source close to Hamas said.

"We have prepared for this battle for two years," said Ali Baraka, the head of external relations for Hamas.

Speaking in a calm voice, Deif said in his recording that Hamas had repeatedly warned Israel to stop its crimes against Palestinians, to release prisoners, whom he said were abused and tortured, and to halt its expropriation of Palestinian land.

"Every day the occupation storm our villages, towns and cities in the West Bank and raid houses, kill, injure, destroy and detain. At the same time, it confiscates thousands of acres of our land, uproots our people from their houses to build settlements while its criminal siege continues on Gaza."

In The Shadows

For well over a year, there has been turmoil in the West Bank, an area about 100 km (60 miles) long and 50 km wide that has been at the heart of the Israeli-Palestinian conflict since it was seized by Israel in 1967.

Deif said Hamas had urged the international community to put an end to the "crimes of the occupation", but Israel had stepped up its provocation. He also said Hamas had in the past asked Israel for a humanitarian deal to release Palestinian prisoners, but this was rejected.

"In light of the orgy of occupation and its denial of international laws and resolutions, and in light of American and western support and international silence, we've decided to put an end to all this," he said.

Born as Mohammad Masri in 1965 in the Khan Yunis Refugee Camp set up after the 1948 Arab-Israeli War, the militant leader became known as Mohammed Deif after joining Hamas during the first Intifada, or Palestinian uprising, which began in 1987.

He was arrested by Israel in 1989 and spent about 16 months in detention, a Hamas source said.

Deif earned a degree in science from the Islamic University in Gaza, where he studied physics, chemistry and biology. He displayed an affinity for the arts, heading the university's entertainment committee and performing on stage in comedies.

Rising up the Hamas ranks, Deif developed the group's network of tunnels and its bomb-making expertise. He has topped Israel's most wanted list for decades, held personally responsible for the deaths of dozens of Israelis in suicide bombings.

A Palestinian prepares a grave to bury the bodies of the wife of Hamas's military leader, Mohammed Deif, and his infant son Ali, whom medics said were killed in an Israeli air strike. (Reuters)

For Deif, staying in the shadow was a matter of life or death. Hamas sources said he lost an eye and sustained serious injuries in one leg in one of Israel's assassination attempts.

His wife, 7-month-old son, and 3-year-old daughter were killed by an Israeli airstrike in 2014.

His survival while running Hamas's armed wing has earned him the status of a Palestinian folk hero. In videos, he is masked, or just a shadow of him is seen. He doesn't use modern digital technology such as smart phones, the source close to Hamas said.

"He is elusive. He is the man in the shadows."