It's going wrong, faster than anyone could have imagined. The army of "liberation" has already turned into the army of occupation. The Shias are threatening to fight the Americans, to create their own war of "liberation".

At night on every one of the Shia Muslim barricades in Sadr City, there are 14 men with automatic rifles. Even the US Marines in Baghdad are talking of the insults being flung at them. "Go away! Get out of my face!" an American soldier screamed at an Iraqi trying to push towards the wire surrounding an infantry unit in the capital yesterday. I watched the man's face suffuse with rage. "God is Great! God is Great!" the Iraqi retorted.

"Fuck you!"

The Americans have now issued a "Message to the Citizens of Baghdad", a document as colonial in spirit as it is insensitive in tone. "Please avoid leaving your homes during the night hours after evening prayers and before the call to morning prayers," it tells the people of the city. "During this time, terrorist forces associated with the former regime of Saddam Hussein, as well as various criminal elements, are known to move through the area ... please do not leave your homes during this time. During all hours, please approach Coalition military positions with extreme caution ..."

So now – with neither electricity nor running water – the millions of Iraqis here are ordered to stay in their homes from dusk to dawn. Lockdown. It's a form of imprisonment. In their own country. Written by the command of the 1st US Marine Division, it's a curfew in all but name.

"If I was an Iraqi and I read that," an Arab woman shouted at me, "I would become a suicide bomber." And all across Baghdad you hear the same thing, from Shia Muslim clerics to Sunni businessmen, that the Americans have come only for oil, and that soon – very soon – a guerrilla resistance must start. No doubt the Americans will claim that these attacks are "remnants" of Saddam's regime or "criminal elements". But that will not be the case.

Marine officers in Baghdad were holding talks yesterday with a Shia militant cleric from Najaf to avert an outbreak of fighting around the holy city. I met the prelate before the negotiations began and he told me that "history is being repeated". He was talking of the British invasion of Iraq in 1917, which ended in disaster for the British.

Everywhere are the signs of collapse. And everywhere the signs that America's promises of "freedom" and "democracy" are not to be honoured.

Why, Iraqis are asking, did the United States allow the entire Iraqi cabinet to escape? And they're right. Not just the Beast of Baghdad and his two sons, Qusay and Uday, but the Vice-President, Taha Yassin Ramadan, the Deputy Prime Minister, Tariq Aziz, Saddam's personal adviser, Dr A K Hashimi, the ministers of defence, health, the economy, trade, even Mohammed Saeed al-Sahaf, the Minister of Information who, long ago, in the days before journalists cosied up to him, was the official who read out the list of executed "brothers" in the purge that followed Saddam's revolution – relatives of prisoners would dose themselves on valium before each Sahaf appearance.

Here's what Baghdadis are noticing – and what Iraqis are noticing in all the main cities of the country. Take the vast security apparatus with which Saddam surrounded himself, the torture chambers and the huge bureaucracy that was its foundation. President Bush promised that America was campaigning for human rights in Iraq, that the guilty, the war criminals, would be brought to trial. The 60 secret police headquarters in Baghdad are empty, even the three-square-mile compound headquarters of the Iraqi Intelligence Service.

I have been to many of them. But there is no evidence even that a single British or US forensic officer has visited the sites to sift the wealth of documents lying there or talk to the ex-prisoners returning to their former places of torment. Is this idleness. Or is this wilful?

Take the Qasimiyeh security station beside the river Tigris. It's a pleasant villa – once owned by an Iranian-born Iraqi who was deported to Iran in the 1980s. There's a little lawn and a shrubbery and at first you don't notice the three big hooks in the ceiling of each room or the fact that big sheets of red paper, decorated with footballers, have been pasted over the windows to conceal the rooms from outsiders. But across the floors, in the garden, on the roof, are the files of this place of suffering. They show, for example, that the head of the torture centre was Hashem al-Tikrit, that his deputy was called Rashid al-Nababy.

Mohammed Aish Jassem, an ex-prisoner, showed me how he was suspended from the ceiling by Captain Amar al-Isawi, who believed Jassem was a member of the religious Dawa party. "They put my hands behind my back like this and tied them and then pulled me into the air by my tied wrists," he told me. "They used a little generator to lift me up, right up to the ceiling, then they'd release the rope in the hope of breaking my shoulder when I fell."

The hooks in the ceiling are just in front of Captain Isawi's desk. I understood what this meant. There wasn't a separate torture chamber and office for documentation. The torture chamber was the office. While the man or woman shrieked in agony above him, Captain Isawi would sign papers, take telephone calls and – given the contents of his bin – smoke many cigarettes while he waited for the information he sought from his prisoners.

Were they monsters, these men? Yes. Are they sought by the Americans? No. Are they now working for the Americans? Yes, quite possibly – indeed some of them may well be in the long line of ex-security thugs who queue every morning outside the Palestine Hotel in the hope of being re-hired by the US Marines' Civil Affairs Unit.

The names of the guards at the Qasimiyeh torture centre in Baghdad are in papers lying on the floor. They were Ahmed Hassan Alawi, Akil Shaheed, Noaman Abbas and Moham-med Fayad. But the Americans haven't bothered to find this out. So Messrs Alawi, Shaheed, Abbas and Fayad are welcome to apply to work for them.

There are prisoner identification papers on the desks and in the cupboards. What happened to Wahid Mohamed, Majid Taha, Saddam Ali or Lazim Hmoud?A lady in a black chador approached the old torture centre. Four of her brothers had been taken there and, later, when she went to ask what happened, she was told all four had been executed. She was ordered to leave. She never saw or buried their bodies. Ex-prisoners told me that there is a mass grave in the Khedeer desert, but no one – least of all Baghdad's new occupiers – are interested in finding it.

And the men who suffered under Saddam? What did they have to say? "We committed no sin," one of them said to me, a 40-year-old whose prison duties had included the cleaning of the hangman's trap of blood and faeces after each execution. "We are not guilty of anything. Why did they do this to us?

"America, yes, it got rid of Saddam. But Iraq belongs to us. Our oil belongs to us. We will keep our nationality. It will stay Iraq. The Americans must go."

If the Americans and the British want to understand the nature of the religious opposition here, they have only to consult the files of Saddam's secret service archives. I found one, Report No 7481, dated 24 February this year on the conflict between Sheikh Mohammed al-Yacoubi and Mukhtada Sadr, the 22-year-old grandson of Mohammed Sadr, who was executed on Saddam's orders more than two decades ago.

The dispute showed the passion and the determination with which the Shia religious leaders fight even each other. But of course, no one has bothered to read this material or even look for it.

At the end of the Second World War, German-speaking British and US intelligence officers hoovered up every document in the thousands of Gestapo and Abwehr bureaux across western Germany. The Russians did the same in their zone. In Iraq, however, the British and Americans have simply ignored the evidence.

There's an even more terrible place for the Americans to visit in Baghdad – the headquarters of the whole intelligence apparatus, a massive grey-painted block that was bombed by the US and a series of villas and office buildings that are stashed with files, papers and card indexes. It was here that Saddam's special political prisoners were brought for vicious interrogation – electricity being an essential part of this – and it was here that Farzad Bazoft, the Observer correspondent, was brought for questioning before his dispatch to the hangman.

It's also graced with delicately shaded laneways, a creche – for the families of the torturers – and a school in which one pupil had written an essay in English on (suitably perhaps) Beckett's Waiting for Godot. There's also a miniature hospital and a road named "Freedom Street" and flowerbeds and bougainvillea. It's the creepiest place in all of Iraq.

I met – extraordinarily – an Iraqi nuclear scientist walking around the compound, a colleague of the former head of Iraqi nuclear physics, Dr Sharistani. "This is the last place I ever wanted to see and I will never return to it," he said to me. "This was the place of greatest evil in all the world."

The top security men in Saddam's regime were busy in the last hours, shredding millions of documents. I found a great pile of black plastic rubbish bags at the back of one villa, each stuffed with the shreds of thousands of papers. Shouldn't they be taken to Washington or London and reconstituted to learn their secrets?

Even the unshredded files contain a wealth of information. But again, the Americans have not bothered – or do not want – to search through these papers. If they did, they would find the names of dozens of senior intelligence men, many of them identified in congratulatory letters they insisted on sending each other every time they were promoted. Where now, for example, is Colonel Abdulaziz Saadi, Captain Abdulsalam Salawi, Captain Saad Ahmed al-Ayash, Colonel Saad Mohammed, Captain Majid Ahmed and scores of others? We may never know. Or perhaps we are not supposed to know.

Iraqis are right to ask why the Americans don't search for this information, just as they are right to demand to know why the entire Saddam cabinet – every man jack of them – got away. The capture by the Americans of Saddam's half-brother and the ageing Palestinian gunman Abu Abbas, whose last violent act was 18 years ago, is pathetic compensation for this.

Now here's another question the Iraqis are asking – and to which I cannot provide an answer. On 8 April, three weeks into the invasion, the Americans dropped four 2,000lb bombs on the Baghdad residential area of Mansur. They claimed they thought Saddam was hiding there. They knew they would kill civilians because it was not, as one Centcom mandarin said, a "risk free venture" (sic). So they dropped their bombs and killed 14 civilians in Mansur, most of them members of a Christian family.

The Americans said they couldn't be sure they had killed Saddam until they could carry out forensic tests at the site. But this turns out to have been a lie. I went there two days ago. Not a single US or British official had bothered to visit the bomb craters. Indeed, when I arrived, there was a putrefying smell and families pulled the remains of a baby from the rubble.

No American officers have apologised for this appalling killing. And I can promise them that the baby I saw being placed under a sheet of black plastic was very definitely not Saddam Hussein. Had they bothered to look at this place – as they claimed they would – they would at least have found the baby. Now the craters are a place of pilgrimage for the people of Baghdad.

Then there's the fires that have consumed every one of the city's ministries – save, of course, for the Ministry of Interior and the Ministry of Oil – as well as UN offices, embassies and shopping malls. I have counted a total of 35 ministries now gutted by fire and the number goes on rising.

Yesterday I found myself at the Ministry of Oil, assiduously guarded by US troops, some of whom were holding clothes over their mouths because of the clouds of smoke swirling down on them from the neighbouring Ministry of Agricultural Irrigation. Hard to believe, isn't it, that they were unaware that someone was setting fire to the next building?

Then I spotted another fire, three kilometres away. I drove to the scene to find flames curling out of all the windows of the Ministry of Higher Education's Department of Computer Science. And right next to it, perched on a wall, was a US Marine, who said he was guarding a neighbouring hospital and didn't know who had lit the next door fire because "you can't look everywhere at once".

Now I'm sure the marine was not being facetious or dishonest – should the Americans not believe this story, he was Corporal Ted Nyholm of the 3rd Regiment, 4th Marines and, yes, I called his fiancée, Jessica, in the States for him to pass on his love – but something is terribly wrong when US soldiers are ordered simply to watch vast ministries being burnt by mobs and do nothing about it.

Because there is also something dangerous – and deeply disturbing – about the crowds setting light to the buildings of Baghdad, including the great libraries and state archives. For they are not looters. The looters come first. The arsonists turn up later, often in blue-and-white buses. I followed one after its passengers had set the Ministry of Trade on fire and it sped out of town.

The official US line on all this is that the looting is revenge – an explanation that is growing very thin – and that the fires are started by "remnants of Saddam's regime", the same "criminal elements", no doubt, who feature in the marines' curfew orders. But people in Baghdad don't believe Saddam's former supporters are starting these fires. And neither do I.

The looters make money from their rampages but the arsonists have to be paid. The passengers in those buses are clearly being directed to their targets. If Saddam had pre-paid them, they wouldn't start the fires. The moment he disappeared, they would have pocketed the money and forgotten the whole project.

So who are they, this army of arsonists? I recognised one the other day, a middle-aged, unshaven man in a red T-shirt, and the second time he saw me he pointed a Kalashnikov at me. What was he frightened of? Who was he working for? In whose interest is it to destroy the entire physical infrastructure of the state, with its cultural heritage? Why didn't the Americans stop this?

As I said, something is going terribly wrong in Baghdad and something is going on which demands that serious questions be asked of the United States government. Why, for example, did Donald Rumsfeld, Secretary of Defence, claim last week that there was no widespread looting or destruction in Baghdad? His statement was a lie. But why did he make it?

The Americans say they don't have enough troops to control the fires. This is also untrue. If they don't, what are the hundreds of soldiers deployed in the gardens of the old Iran-Iraq war memorial doing all day? Or the hundreds camped in the rose gardens of the President Palace?

So the people of Baghdad are asking who is behind the destruction of their cultural heritage: the looting of the archaeological treasures from the national museum; the burning of the entire Ottoman, Royal and State archives; the Koranic library; and the vast infrastructure of the nation we claim we are going to create for them.

Why, they ask, do they still have no electricity and no water? In whose interest is it for Iraq to be deconstructed, divided, burnt, de-historied, destroyed? Why are they issued with orders for a curfew by their so-called liberators?

And it's not just the people of Baghdad, but the Shias of the city of Najaf and of Nasiriyah – where 20,000 protested at America's first attempt to put together a puppet government on Wednesday – who are asking these questions. Now there is looting in Mosul where thousands reportedly set fire to the pro-American governor's car after he promised US help in restoring electricity.

It's easy for a reporter to predict doom, especially after a brutal war that lacked all international legitimacy. But catastrophe usually waits for optimists in the Middle East, especially for false optimists who invade oil-rich nations with ideological excuses and high-flown moral claims and accusations, such as weapons of mass destruction, which are still unproved. So I'll make an awful prediction. That America's war of "liberation" is over. Iraq's war of liberation from the Americans is about to begin. In other words, the real and frightening story starts now.

Robert Fisk: For the people on the streets, this is not liberation but a new colonial oppression

America's war of 'liberation' may be over. But Iraq's war of liberation from the Americans is just about to begin