While the world focused on Osama bin Laden as the No. 1 fomenter of terrorism, another more hands-on, in-the-field jihadist was being shaped.

Now Abu Musab Al-Zarqawi either claims or is blamed for every atrocity in Iraq from suicide bombings to the brutal beheading of hostages. His ultimate goal? A bloody - but purifying - civil war.

We're still in the chalky hills of Amman. But driving north, the desert chic of the Jordanian capital quickly fades to become the cinder-block grime of a sprawling industrial quarter. Here, helpful locals urge us to keep the car doors locked - even as we drive around. There are only a few roadside hawkers - their grapes, watermelons and luscious figs stewing in the midday sun; and a couple of katip men are idle - they sit under faded calico umbrellas with battered typewriters on rickety card tables, waiting for illiterates who'll pay them to write a letter or fill out a form.

Any doubt we've crossed into a different place and space is expunged when Bilat, the driver, slows his clapped-out Kia minibus to negotiate a ruptured and flooding sewer line. As a foul odour fills the bus, he jokes: "Ah, French perfume..." A few hundred metres down the hill, after a threadbare mosque that has none of the customary glitter of the well-heeled end of town, and beyond idle factories and fences festooned with litter that couldn't get away, he formally declares: "This Al-Zarqa ... the home of Abu Musab Al-Zarqawi."

The US has a $25 million ($A35 million) bounty on Zarqawi's head. And Washington now bills him as the spearhead of the bloody insurgency that is wrecking virtually all efforts by the US military and the Washington-backed interim regime in Baghdad to assert authority or to impose security in "liberated" Iraq. He has strewn fear throughout a war-numbed nation and a nervy and restless foreign community in Baghdad as grainy videos reveal him personally hacking off the heads of terrified hostages - reading aloud religious tracts and threatening more death.

Zarqawi and the small army he calls Tawhid Wa'Al-Jihad have expanded their area of operations, taking control of vital thoroughfares in the capital and forcing swaths of country to be declared no-go zones for US forces. At the same time, Zarqawi wrestles with nationalist Iraqi fighters for control of the insurgency's post-Saddam agenda. American crackdowns have little success in curbing the crisis.

Since Zarqawi bounced out of relative obscurity last year, he has been linked to an appalling litany of violence. The attacks range from the horribly grotesque, like the beheading of the Jewish-American businessman Nick Berg in May 2004 which he celebrated by releasing a video titled Sheik Abu Musab Zarqawi Slaughters an American Infidel, to a barrage of audacious car and truck-borne suicide bombings that have killed a high-profile United Nations envoy, dozens of prominent religious and political figures and hundreds of ordinary Iraqis. Zarqawi has masterminded or inspired the capture of more than 130 foreign hostages in Iraq. Last month the world was forced to hold its breath as two Americans and a British hostage pleaded for their lives, before Zarqawi himself, according to CIA analysis of the web footage, callously cut the throats of the struggling Americans. Then he roughly decapitated them, holding the heads up for the cameras - and, with a nonchalant twist of the knife, gouged out one of the victim's eyes.

While a separate insurgency group dangled the lives of two young women hostages from Italy - they were subsequently released - Zarqawi imposed a calculated silence on the fate of the Briton who had been snatched with the Americans - 62-year-old Kenneth Bigley. It was broken a week later only by the release of another harrowing video of a distraught Bigley, shackled and kneeling in a cage as he pleaded with Prime Minister Tony Blair to spare his life. But Zarqawi knew that he was filling the media space in Britain and around the world with bestial but cost-effective propaganda that would work for him on two levels.

Zarqawi has his own sophisticated PR machine, which talks him up as the single cause of all that is violent in the new Iraq - just as much as the Washington spin doctors do. The Zarqawi profile is so great now that it ceases to matter how many of the charges against him are true; what does matter is that he has become an inspirational figurehead for an insurgency army of as many as 20,000 fighters that has been able to dig in, establishing operational practices and lines of funding and communication for what many observers fear will be Iraq's descent into a bloody civil war.

The most troubling aspect of Zarqawi's arrival on the battlefield is that he has the determination and ideological baggage needed to manipulate all sides to start an all-out war.

Any quest to discover Zarqawi's past is not the story of just one person. It is also a journey into a fearsome philosophy that is being used to breach the Islamic convention that Muslims should not act violently towards each other.

It is called the Salafi movement, the credo of the fundamentalist Islamic warmongers that provides the religious sanction without which violence could not be perpetrated in the name of Islam. Salafi thought might have languished ineffectually on the fringes of world affairs had not the US decided in the 1980s to pour billions of dollars in arms and support into an earlier but very different "coalition of the willing" - an informal, pan-Arabist army of volunteers that fought to end the Soviet occupation of Afghanistan.

That 10-year-long struggle was justified religiously on the grounds that all Muslims had a duty to repel the infidel Soviet invasion of Muslim Afghanistan. But it was a further refinement by Zarqawi's prison-cell mentor, the 44-year-old Abu Mohammed Al-Maqdisi, that made it possible to encourage the veteran Arab warriors from Afghanistan to gird themselves for other battles; and it was in Afghanistan that Osama bin Laden and Zarqawi learned the undeniable truth of asymmetric warfare - that a bunch of uneducated youths armed only with credit cards and box-cutters could take the modern US empire by the throat; that a few cars loaded with fertiliser could stop that empire's technologically sophisticated army in its tracks.

Hardly anyone knows what Zarqawi really looks like. The US "wanted" posters list his height and weight as unknown. The same old passport-like pictures are pasted up: round face, furtive eyes, stubbled chin and beanie-like cap. By many accounts, he is not especially bright, but he wears his emotions close to the surface. Accounts of his early days suggest he is prone to tears, sometimes in discussions about God.

Much of what is known about him comes from the prisoners who shared a Jordanian cell block with him for five years after he was convicted in 1994 of plotting to overthrow the regime of King Hussein. A former inmate from Swaqa Prison told me Zarqawi burst into sobs when he rebuked him for beating up another inmate. Yousef Rababa, a teacher of Islamic religious studies who served time for plotting a bombing mission in Israel, said the only softness he saw in Zarqawi was towards his mother.

In a reception room in his comfortable middle-class home high on one of the rolling hills over which the Jordanian capital is draped, Rababa said that when his mother visited, Zarqawi would shower, dress in his cleanest clothes and wear cologne. Sitting in an adjacent cubicle, the teacher eavesdropped on some of the mother-son meetings: "He was always seeking her forgiveness and blessings; he'd wish her happiness, too."

Zarqawi's acts of violence in the past six months have taken him into the lounge rooms of the world. But nobody, least of all the Americans, is sure of where he hides in Iraq. It seems implausible that he would base himself in Falluja, the Sunni city that has refused to surrender to US force. But late last month the London-based daily Al-Hayat published an interview with an unnamed Zarqawi associate who claimed to have met Zarqawi there "recently". The US insists he is there, too, but there have been no confirmed sightings and constant and powerful bombing of what the US describes as Zarqawi safe houses has so far failed to curb the rate of insurgency attacks, to turn up a body, or to prompt a claim for Washington's ransom from anyone who might have tipped them off to Zarqawi's whereabouts.

It is noon and the backstreets are virtually deserted. Zarqawi's family still lives in an area called Al-Kasara, where the dusty, mottled sprawl of Al-Zarqa runs abruptly into the wall of an abandoned quarry on one side and an old cemetery on another. In the street where the young Zarqawi kicked a ball, a child labours to get a kite aloft. But there is no response to my banging on a heavy metal gate set in a wall that surrounds the family's drab two-storey house. There's a satellite TV dish and a lonely olive tree. Across the way, rubbish spills from a dumpster.

A few of the neighbours straggle towards the Al-Falah mosque for prayers - this was where Zarqawi spent much of his time. "They don't talk," a passer-by volunteers about the family, and others explain why. Zarqawi's brother-in-law, Salih Al-Hami, had spoken publicly a few weeks earlier and still had the bruises from a doing over by Jordanian security service officers.

A circumspect shopkeeper, who gave his name as Abu Mouad S'waha, says the mukhabarat - the collective name by which Arabs refer to all security agents - had been making more visits to the area as Zarqawi's activities in Iraq drew more attention, and were warning people not to talk to outsiders about Zarqawi. "They think they can shut down the story," the shopkeeper says.

The locals are cautious - the shopkeeper the only one to give his name - but they all talk: some worry that the character beaming back from Iraq by news satellite is so big that he must be a creation of US propaganda; but all, it seems, want visitors to acknowledge their pride in Zarqawi. "How did such a normal guy become so big?" asks a man outside the mosque. "We pray for him, because he is one of us," another with a bushy white beard tells me.

And despite the pervasive reticence, they offer up the essentials of the Zarqawi story, which varies from "local boy makes good" to "who'd have thought he had it in him?"

Some of them see great symbolism in the proximity of the local cemetery to Zarqawi's home. As a restless teenager he emerged as a hard-drinking, knife-wielding tough who was not greatly interested in school or religion.

His father was the local muktar, an unofficial community counsellor from whom people sought advice. But his father's early death thrust added responsibility on the young Zarqawi. One of the locals explained for

Good Weekend: "The only way to survive in Al-Zarqa was to be tough [and] he had a duty to protect his family, especially his sisters." Another says that one night in his teens, Zarqawi drank so much that he fainted - and that when he came to, he vowed: "Never again."

The young Zarqawi worked for a time in the municipal electrical service. He soon drifted out of that job, but mystery surrounds just how he ended up in Afghanistan in 1989. For years, the Saudi government had been paying young Arabs to fight in Afghanistan, but by then the Soviets were in retreat from a conflict that had become their Vietnam. There are reports that Zarqawi fought to drive the Russians out of the eastern city of Khost, near where bin Laden would later locate some of his training camps. But others refer to him only as an aspiring writer for a magazine called Al Bonian al Marsous, "The Strong Wall". They say he listened closely, but kept to himself.

Before he was silenced by the Jordanian authorities, Salih Al-Hami, Zarqawi's brother-in-law, told the Arabic television channel Al-Jazeera that Zarqawi had been a sponge for Salafi literature in Afghanistan, but had been reluctant to join any of the battlefront groups - particularly Osama bin Laden's al-Qaeda.

Zarqawi returned to Jordan in 1992, confused by emerging signs of a protracted civil war in Afghanistan in the wake of the Arab triumph that Salafi philosophers had promised would deliver an Islamic nirvana. Some who observed him at the time thought he was ripe for the hardline speeches of Al-Maqdisi, the Salafi scholar who also was from Jordan.

These two had met in Pakistan and together they set up Beit Al-Imam, a help group for fighters returning to Jordan from Afghanistan. It was hardly surprising that many of the fighters were looking for a new cause: bin Laden found his in Saudi Arabia - in Riyadh's deepening military reliance on the US; and for Al-Maqdisi and Zarqawi it was the social and economic malaise threatening to sink Jordan in the wake of the 1990-'91 Gulf Crisis.

The journalist Abdullah Abu Rumman soon detected a strident new message in Jordanian discourse: "Al-Maqdisi's speeches were full of fire. He condemned the government and he branded the Sunni clerics as instruments of the regime; he called them taghout - this was the first time we'd heard this old word used to describe Muslims as infidels."

A Kuwait-born Palestinian, Al-Maqdisi's real name is Isam Al-Barqawi. He studied physics and chemistry in Baghdad as a young man, but abandoned his course to go to Medina, in Saudi Arabia, to take up the religious studies that would shape his Taliban brain.

His two wives still live at Rusaifeh, in the urban corridor between Al-Zarqa and Amman. In his absence, his house is said to run much as Zarqawi's does - the children are barred from attending school and are made to study only religious texts at home. TV is forbidden. And when Al-Maqdisi was hauled before Jordan's State Security Court recently, there were audible gasps when, brimming with pride and emotion, he announced that his 14-year-old son had died fighting with the insurgents in Iraq.

In 1994, Al-Maqdisi was jailed amid rising fears among officials in Amman over the growing band of followers inspired by his rants against the regime. On being convicted of plotting the overthrow of the Jordanian government, Al-Maqdisi was sent down for 15 years. His jailing would be the making of Abu Musab Al-Zarqawi, who went into the slammer with him - on the same charges.

Swaqa Prison sits alone, on the edge of a highway that cuts like a ribbon of steel through the Jordanian desert, running south from Amman to the Red Sea port of Aqaba. It was a menacing place where prisoners were forced to cluster according to their beliefs - political and religious, or around leaders they thought would protect them from violence. Inmates say Al-Maqdisi and Zarqawi gathered their supporters in a tight knot under Al-Maqdisi's leadership.

The section of Swaqa that housed political prisoners had four dormitories with bunk bedding for about 30 prisoners in each.

Al-Maqdisi took over a whole dormitory which became his tiny, Taliban-like lair. As

his lieutenant, Zarqawi was the enforcer of a strict code of conduct: group members had to seek permission to talk to other prisoners; their book reading was censored (Zarqawi punished a prisoner for reading Crime and Punishment) and the only press reports they had were clippings on events in Afghanistan; they could listen to the TV news, but the screen was permanently covered lest they see a woman newsreader.

In the middle of all this was Zarqawi's "tent" - he had draped the sides of his lower bunk bed with blankets, screening out the world as he laboured over the Koran.

The group was barred from organised sport with other prisoners and was made to exercise in a makeshift gym in which Zarqawi had fashioned weights from tin buckets of rocks strung on lengths of timber. To leave the group was to be sentenced to solitude for the rest of the term; to join others was an act of betrayal that met a violent response.

Several former inmates claimed Swaqa was the sort of place where, for sport, the warders would cuff prisoners to a hook high on a corridor wall so that passing officers could take out their frustration by beating them. Inmates said that in such cases, Zarqawi would attack an approaching officer to draw his attention away from the cuffed prisoner. "He was very brave - when I arrived at Swaqa he was already in solitary," one of them told me.

Members of the Al-Maqdisi-Zarqawi group were required to dress in the same Wahabbi style - the scraggy beard, short hair on their heads, dishdashas that came to just below their knees and, always, the black head-cloth that was the uniform of the Taliban in Afghanistan. Rababa the teacher said it was a hard group to penetrate, but had bargaining power in the form of money from outside donations.

Zarqawi took to giving passionate sermons on Fridays, usually on the failings of the Jordanian regime. He had none of Al-Maqdisi's charisma, but commanded the respect of his followers.

The majority view among the prisoners was that in those early days, Zarqawi was a deputy to Al-Maqdisi. A former inmate warned by the Jordanian authorities not to be interviewed nevertheless told Good Weekend: "We just didn't believe that he was, or would become, important. For our group, Al-Maqdisi was the important figure and we used to spend time trying to understand his ideology because it was extreme stuff - he was saying that the king and the Jordanian army and other security services were infidels and therefore it was right to use force against the regime. But Zarqawi had no ideas of his own, just whatever Al-Maqdisi fed to him. So we had the main guy there to talk to - why would we waste time with Zarqawi?"

But Zarqawi was not going to be anyone's No 2 for long. Several former inmates recounted a power struggle in which Al-Maqdisi's sullen and serious pupil challenged his control of the group.

In Jordanian parlance, Zarqawi was the only "East Banker" in the group. This was a critical advantage in his struggle with Al-Maqdisi. To come from the east bank of the Jordan River meant Zarqawi was of the powerful tribes that are the bedrock of the Jordanian establishment - he was of the legendary Beni Hassan tribe that watched over Jordan's border with Iraq and had delivered national leaders and many who served in the military and the intelligence services. Unlike the dislocated Palestinian Al-Maqdisi, Zarqawi's life was not governed by an instinctive fear of state officials - particularly the police and intelligence services.

But Zarqawi had another advantage. Both he and Al-Maqdisi were treated as heroes of the Afghanistan war. However, Al-Maqdisi had done his religious philosophising from Peshawar. That city certainly was a gateway to the Afghan theatre of war, but was located well inside the borders of neighbouring Pakistan. So as the only true Afghan veteran in Swaqa, Zarqawi's pedestal was that little bit higher.

A fellow inmate recollects the differences between the two, noting Zarqawi's blunt ideological persistence: "Al-Maqdisi could discuss literature, poetry and politics with all the confidence of his education, but Zarqawi knew none of this ... just the Koran, which he memorised in prison - all 6000-plus verses."

In contrast to Al-Maqdisi, Zarqawi subjected newcomers to a sudden-death assessment: "He'd talk to new prisoners, check their views on the regime and the police and decide very quickly if they were good Muslims or infidels, and whether or not they could join his group."

As the leader of another inmate group, the teacher Rababa met for frequent discussions on prison issues with both Al-Maqdisi and Zarqawi. He observed the widening personal rift between them. "Zarqawi told me that Al-Maqdisi had a behavioural problem," he recalls. "He accused him of selfishness and of negligence in his religious observances. Zarqawi saw Al-Maqdisi as two-faced because he was a religious scholar who also had a love of life." As Rababa saw it, Zarqawi was the opposite: "He loved his growing authority; everything had to be so serious, and his instinctive response if he felt threatened or cornered was to lash out. He had a strong personality, but Zarqawi didn't seem to have a vision for the future. His ideology was limited and his arguments in defence of it were even more limited - he had no interest in a dialogue. At the end of the day he was just like Bush, telling us, 'You are with me or against me.'"

The other prisoners were struck by the number of disciple-like visitors who came to see both men - and the weight of the business they discussed and what it revealed of Al-Maqdisi's power and influence. One told me a group of Saudi Arabians had come to receive Al-Maqdisi's religious blessing before the explosion of a 1500-kilogram-plus truck bomb at the Khobar Towers residential complex in Riyadh in 1996 - where 19 US servicemen died and almost 400 others were injured. The Khobar attack has come to be seen as the opening strike in a campaign that has effectively driven the US military out of Saudi Arabia.

Another cell-block colleague saw the difference in the two men's propensity for violence: "Al-Maqdisi was a coward ... afraid of the warders. It was always Zarqawi, who was physically stronger, who went on the front foot confronting the guards."

All the time Al-Maqdisi was watching Zarqawi, seemingly aware that he was being undermined, but unable to do anything about it. It was about four years after their arrival at Swaqa that prisoners outside the Beit Al-Imam group realised Zarqawi had slid into the leadership. Rababa the teacher observed that by the time of their release, Al-Maqdisi and Zarqawi no longer spoke to each other.

After his release, Zarqawi was back on the streets and in the mosques of Al-Zarqa. Unhappily, according to his brother-in-law: "I felt he was bored; I felt he was bitter. I felt the spirit of jihad inside him. He was dying to get out of this country."

Jordanian intelligence had a special unit to monitor the activities of Jordanians, like

Al-Maqdisi and Zarqawi, who had become Afghan Arabs. According to a well-placed observer in the Jordanian capital, the unit had a clear task: "Harass these guys to make it difficult for them to get jobs and, hopefully, to drive them out of the country. They blocked whatever Zarqawi wanted to do - at one stage he tried to buy a pick-up from which to sell fruit and vegetables, but they would not give him the paperwork. They were always harassing him, pulling him in for interrogation."

The Amman lawyer who had represented Zarqawi at his trial, Mohammed Al-Dweik, saw what was happening: "He came to see me. He wanted to live here and work here and to have a family - but the Interior Ministry would not give him the paperwork. Here in Jordan we beat and torture people like Zarqawi and make them want to leave the country - so he went back to Afghanistan."

But here there was something that didn't quite add up in Zarqawi's story - a period in which he cooled his heels, perhaps deciding on what course his life should take. The thug and firebrand of Swaqa left prison brimful of Al-Maqdisi's war cries and then stormed off to Peshawar which, early in 2000, was still the gateway to what by then had become Taliban-controlled Afghanistan.

Crossing the border should have been a doddle, but he seemed to hesitate, instead bringing his sick mother to Pakistan - hoping the air would be better for her. And when he finally headed west through the Khyber Pass, it was because he was forced to after Pakistani authorities arrested him for overstaying his six-month visa.

He was jailed briefly and ordered to leave the country. Jordan was no longer an option as he had been named there as a suspected terrorist, so Zarqawi packed his mother back to Amman, where she died early this year as she prayed that her son would die in battle, according to The New York Times. Zarqawi headed for Kabul.

It seems to have been a turning point, and he chose the moment to abandon his old identity, so well-known to authorities in Jordan, as he entered a new theatre of war. Having previously lived and travelled under his birth name, Ahmad Fadil Al-Khalayilah, Zarqawi decided to honour his home town, Al-Zarqa, by taking "Zarqawi" as his nom de guerre. He arrived in Afghanistan a year or more before 9/11 and the start of the US war on terror.

The question the Americans would like answered is whether Zarqawi has struck any sort of deal with Osama bin Laden. What happened on his return to Afghanistan and his movements since then are murky. Al-Jazeera television reported that Zarqawi fought with al-Qaeda in the last big battles in Afghanistan, including the US assault on Tora Bora. But in June, US Secretary of Defence Donald Rumsfeld undercut much of Washington's argument of a link when he said of Zarqawi: "[He] may very well not have sworn allegiance to [bin Laden]. Maybe he disagrees with him on something; maybe because he wants to be 'The Man' himself." And in the Al-Hayat interview published in September, Zarqawi's unnamed associate was quoted as saying: "I wish he was al-Qaeda's representative in Iraq. But the truth is he has his own organisation, he is not an al-Qaeda member and he has no connection with Osama bin Laden."

Clearly, Zarqawi would have needed the Taliban's blessing to operate in Afghanistan before 9/11. But he did seem to be in pursuit of an agenda different from that of bin Laden. He set up a jihadist training camp at Herat in the west of Afghanistan, far away from bin Laden's camps on the eastern frontier with Pakistan. He complained to family friends that senior al-Qaeda types worried that he was too strict on his followers; he objected to their acceptance of Saudi donations; and he intimated it was the patronage of an Afghan warlord that had made his Herat camp possible.

But being in Herat put Zarqawi closer to the north-east corner of Iraq. This was an area protected from the regime of Saddam Hussein by the US-imposed no-fly zone. It was here that a small group of the so-called Afghan Arabs worked with local Kurdish fundamentalists to set up a Taliban-style fiefdom in the name of Ansar Al-Islam. Washington argued that this was in fact a fallback set up by al-Qaeda in the knowledge that after the 9/11 attacks it would not be able to work from Afghanistan.

But the evidence was inconclusive when the camps were raided as a part of the US invasion of Iraq. There was proof of experimentation in small-scale chemical terrorism but conflicting intelligence assessments on whether Zarqawi himself had been stationed in the camps.

People living near the Ansar Al-Islam camps claimed Zarqawi arrived soon after the 9/11 attacks and that he was an agent of al-Qaeda. A farmer told Al-Jazeera: "This house that you see behind me was built by the Ansar. Zarqawi, representative of Osama bin Laden, used to live here." Mohammed Rumman, a brother of the journalist Abdullah Abu Rumman, is doing a doctoral thesis on the Salafi movement. He says his sources have persuaded him it was the arrival of Zarqawi that moulded the camps into the sort of facility that might have turned out fighters who are now playing key roles in the Iraqi insurgency.

The US claims Zarqawi was close to Saddam's Baghdad and had been to the Iraqi capital to be treated for wounds from a US missile strike in Afghanistan. But Rumman believes Zarqawi remained in the north till after the fall of Baghdad in April 2003. Zarqawi has been so contemptuous of the Saddam regime and the Baath Party, which he dismissed earlier this year as "infidels" and "weaklings who can't fight for themselves", that it is difficult to see how they might have worked together. Laith Shubaylat, an outspoken Amman lawyer, who was in Swaqa Prison with Zarqawi, told me: "He can deal only in black and white. He is so utterly inflexible I'd say it's impossible for him to work with the Baathists - you'd have to show me the video of the gun to his head before I could see him working with Saddam."

Jordanian security officials claim Zarqawi illegally re-entered his homeland through Syria late in 2002 - about a year after 9/11. A month later, US diplomat Laurence Foley was murdered. Three men were arrested, and all allegedly told investigators that Zarqawi had been the operation's instigator. It was his first entry into the Western media consciousness.

Five months later, Colin Powell made a now widely discredited speech before the United Nations justifying Washington's planned invasion of Iraq, in which he claimed Zarqawi was a bin Laden "associate and collaborator" who was part of a "sinister nexus between Iraq and the al-Qaeda terrorist network".

Zarqawi's old Amman lawyer, Mohammed Al-Dweik, told me: "I stayed in touch with the client that I knew as Ahmad Fadil Al-Khalayilah till he disappeared off to Afghanistan and it wasn't till last year, when Colin Powell told the UN, that I knew there was a terrorist called Zarqawi. And a couple of days later I had a call from his mother to tell me that my client was the man in the news."

The US was warned that its invasion of Iraq would create a terrorist honey pot - and this was just what Zarqawi had been looking for. The early targets in the resistance were conventional - the US military and those Iraqi institutions deemed to be collaborators, such as police stations. But the bombing of the Jordanian Embassy in Baghdad in August last year signalled a critical new turn - and that a new hand seemed to be at work.

The blast was so powerful it destroyed the vehicle in which it was planted - no one could tell if it was a car, a bus or a truck. As many as a dozen people died and in the chaotic aftermath an Iraqi crowd stormed the building, destroying pictures of King Abdullah and his late father, King Hussein. US forces raced tanks and Humvees into place, leaving a circle of about 100 metres in diameter which was littered with body parts from the dead and injured and their wrecked cars. I was in Baghdad at the time, and I climbed onto the roof of an adjacent building to get a better view. Looking down, the circle looked like the first ripple going out in a campaign that would claim many more lives and would be felt way beyond the dusty confines of Baghdad.

All the dead were Iraqis. And perhaps because no Jordanian diplomats died and the building was not so badly damaged, the realisation that this was the start of a brutal new campaign by a new player was reserved for a bomb two weeks later at the UN's Baghdad headquarters. Zarqawi became the only and immediate suspect, in part because the embassy strike was a gory and personal double hit. Apart from being the first major insurgency bombing since the invasion of Iraq, it struck at the heart of the Amman regime which Zarqawi hated for its lack of Islamic purity and alliance with Washington.

Now, Zarqawi either claims or is blamed for every atrocity in Iraq - and several beyond its borders. Moroccan intelligence believes he may have helped organise the Madrid train bombings in March; the Germans say they have sprung a cell whose members were trained at Zarqawi's Afghanistan camp; and the Jordanians claim he was behind a plot in April this year in which 20 tonnes of chemicals were to be detonated in Amman, producing a poison cloud that could have killed 80,000 people. Whether Zarqawi has the muscle to run such a terror network across the world is an open question.

Unlike bin Laden, who has positioned himself more as a head-office strategic operator, Zarqawi is a hands-on, in-the-field jihadist.

US and other intelligence services have concluded from some of the beheading tapes that it is Zarqawi who is holding the knife and his voice making the announcements.

In a tape aired on Al-Jazeera, Zarqawi spelt out his agenda: "We are invading them, just as they are invading us; and we are attacking them, just as they are attacking us; and we are hurting them, just as they are hurting us." Soon after, he celebrated all that he claims as his work, and the rest of which he is accused, in another chilling audio recording: "God honoured us and so we harvested their heads and tore up their bodies in many places: the coalition forces in Karbala; the Italians in Nasseriyah; the US intelligence in Al-Shahin Hotel; and last, but not least, what God has honoured us with today: the Polish forces in Hilla."

There are, however, signs of tension between Zarqawi and the dozens of Iraqi insurgent groups that have emerged since last year's invasion. There were internet death threats against Zarqawi after a wave of attacks on Iraqi police stations earlier this year. Good Weekend was also told by sources in Falluja recently of

an organised movement that hoped to drive foreign fighters out of the war-torn city.

But some insurgency groups claim to be inspired by Zarqawi, fighting in his name without a direct link, in much the same way as the bin Laden brand of terrorism has been franchised around the world. Fighters who took to the streets in Baqaba, north of Baghdad, as part of a wave of tightly co-ordinated strikes that killed more than 100 people in the days before the June 28 establishment of Iyad Allawi's interim government wore headbands proclaiming their support for the Jordanian. Meanwhile, one of the more hardline Sunni mosques in Baghdad has been renamed to honour the medieval Muslim philosopher - Taqi Al-Din Ahmad Ibn Taymiyya - whose brutal religious justifications for war are the core of Salafi thought and the Zarqawi campaign.

Mohammed Al-Dweik, Zarqawi's lawyer in Amman, has vivid memories of being lectured by his client on his conversion to the brittle Salafi thinking that now underpins his every move. In a recent, late-night meeting on the terrace at the Four Seasons Hotel in Amman, he recalled how Zarqawi showed off what he had absorbed during his time with Al-Maqdisi: "He'd tell me that the Arab homelands were like fields - farmers' fields; that our leaders worked the fields for the US and that we, the Arab people, were their cows and donkeys." And like so many others in Jordan, Al-Dweik insists that Al-Maqdisi is the key to understanding Zarqawi, describing the scholar as "the most dangerous man in the whole Middle East". The lawyer said that what made Al-Maqdisi such a threat to the region was his single-handed revival of the warrior and religious teachings of the 14th-century scholar Taqi Al-Din Ahmad Ibn Taymiyya, and the impetus that revival had given to the Salafi movement.

Zarqawi's agenda is not a simple demand that US forces leave Iraq. It is also about who should be allowed to run the country and even to live in it. Zarqawi believes the Allawi interim government must be eliminated, not just because of its association with the US but because it fails his Salafi test of religious purity. That is why Zarqawi has already issued a personal threat against the life of the interim prime minister. But under the arcane principles of Salafi thinking, Shiite Muslims - who make up about 65 per cent of the Iraqi population and are determined to take over the running of the country - are also deemed to be "infidel", and they, too, are Zarqawi targets.

Such are the strictures of this philosophical straitjacket that even though Zarqawi himself is a Sunni, he is opposed to the regime of the ousted Saddam Hussein and his Baath Party, both of which were Sunni but far too secular in their outlook for Zarqawi's liking. The Zarqawi world view is ferociously fundamentalist and allows for the survival of only the few who embrace his extremist Salafi doctrine.

The core Salafi belief, best exemplified by the Taliban in Afghanistan, is that only those who knew the Prophet Mohammed and the next three generations could have acquired a pure sense of what Mohammed understood of Islam. Any change outside that ancient narrow window is deviant behaviour that must be stamped out. But the philosophy divides again in terms of the perceived threats to Islam and, more importantly, the duty of individual Muslims to counter such threats. Do the threats reside only in a foreign, non-Islamic invader, like the US? Or is there an internal threat to Islamic purity in Muslim governments, be they tradition-based, like Saudi Arabia and Jordan; or puppet regimes installed by foreign force, as in Iraq and Afghanistan? Or, as Zarqawi is arguing in Iraq, whole classes of people like the country's Shiite majority?

None of these finer points was understood when Zarqawi first came to the attention of analysts and commentators, who conveniently bundled him in with al-Qaeda. But within the relativities of Islamic terror, Yousef Rababa, the teacher who did time with Zarqawi in Swaqa Prison, argues that bin Laden is less of an extremist than Zarqawi. To Westerners, it might seem like splitting doctrinal hairs, but the teacher told Good Weekend: "bin Laden sees Americans and Jews as the enemy, along with the foreigners who are in the Arab homelands. But in prison, Zarqawi told me that anyone we think is not a believer is the enemy - and that can be Arabs, too, especially Shiites."

Despite the ghoulish beheading tapes, Zarqawi is still much of a chimera. Given his philosophical opposition to so many of the factions around him, his support base in Iraq is not easily understood - other than that it is based on the old adage that "mine enemy's enemy is my friend".

Each tape he releases is pounced upon by teams of US experts who have concluded that most are genuine. But others take an interest, too. Many who did prison time with Zarqawi harbour doubts that this is the man they knew. The release of each tape sparks a ring-around among former inmates of Swaqa and others who have known Zarqawi, as they attempt to match the voice with that of their former cell-mate. There is much scepticism. His lawyer, Mohammed Al-Dweik, pulled at his own lower lip and tongue to mimic the sounds and patterns of his client's speech which he says are absent from the recordings. One of them added: "How do you go from being almost illiterate to near-genius? Personal limitations would make it impossible for someone like him to carry on a war in a country he doesn't know."

But perhaps the best insight into Zarqawi's thinking is a controversial letter recorded on a CD found in the possession of a suspected insurgency courier captured by Iraqi intelligence officers in the north of Iraq in January. American intelligence has seized on the letter because it was addressed to Osama bin Laden, underpinning Washington's claim of a relationship between bin Laden and Zarqawi.

However, there is only a bare hint of a master-servant relationship in the letter, which reads more like that of one chief executive to another on how to take advantage of a market opportunity: "We do not see ourselves as fit to challenge you ... [but] if you agree with us ... we will be your readied soldiers, working under your banner, complying with your orders, and indeed swearing fealty to you publicly and in the news media ... if things appear otherwise to you, we are brothers, and the disagreement will not spoil [our] friendship."

If it is genuine, this letter is of greater interest for what it reveals about Zarqawi and his plans to foment civil war in Iraq. The author uses classic flowery language to signal his plan to provoke a Muslim-on-Muslim civil war, when he says of the majority Shiite population: "They are the insurmountable obstacle, the lurking snake, the crafty and malicious scorpion and the penetrating venom ... they are the enemy ... the bone in [our] throats ... if we succeed in dragging them into ... sectarian war, it will become possible to awaken the inattentive Sunnis as they feel imminent danger and annihilating death at the hands of these Sabeans. The only solution is for us to drag the Shiites into battle ... to strike the religious, military, and other cadres among the Shiites with blow after blow until they bend to the Sunnis."

When the letter is read with an understanding of the Salafi dogma so fiercely held by Zarqawi, it becomes truly frightening. It warns of the approach of "zero hour" - June 30 - which then was the date Washington proposed handing some power over to an interim government. It harangues: "If we are able to strike [the Shiites] with one painful blow after another until they enter the battle ... if you knew the fear [for their future] among the Sunnis, your eyes would cry over them in sadness."

The emerging pattern of violence in Iraq is dishearteningly similar to the Algerian civil war of the 1990s. That was a conflict that claimed more than 60,000 lives in an unbridled application of Salafi-sanctioned Muslim-on-Muslim violence. The US-backed Algerian regime was attacked on the basis that it was a foreign lackey; Muslim civilians who sided with the regime or simply sat on their hands were deemed to be fair game because, as the Salafis would have it, by not defending Islam they were being un-Islamic; and the media, schools, missionaries and foreign individuals and companies all became targets.

Perhaps this is the challenge Zarqawi has set for himself in Iraq. The most sober intelligence assessments say he has a force of no more than a couple of hundred fighters - Jordanian and other Arab nationals. He can't do it all by himself, but there is a risk that the religious and other divisions that exist already in Iraq are so deep and treacherous that a campaign of well-targeted violence could provoke Iraqis into doing the job for him.