The trail from the Madrid bombs leads to Britain, Norway and many points beyond

On a routine patrol day in late February, two Spanish police officers stopped a Volkswagen on its way from the northern mountains of Asturias to Madrid. They fined its driver for a minor traffic offence and ran a check on the number plate before waving the car on its way.

On a routine patrol day in late February, two Spanish police officers stopped a Volkswagen on its way from the northern mountains of Asturias to Madrid. They fined its driver for a minor traffic offence and ran a check on the number plate before waving the car on its way.

Little did they know the car contained men on their way to take part in Spain's deadliest ever terrorist attack. Nor could they know the Moroccan driver and his passengers were in a stolen car: the car's owner had not yet reported its theft.

It was a missed chance to foil the Madrid bombings of 11 March that killed 191, injured more than 1,800, toppled the Spanish government and spread fear across Europe.

Yesterday, the Interior Ministry released details of an al-Qa'ida videotape which threatens more terrorist attacks in Spain and singles out the incoming Socialist government for its decision to send more troops to Afghanistan,

The video was found in the rubble of an apartment where seven suspects in the bombings blew themselves up on 3 April as police prepared to enter.

In the video, three of the suicide terrorists claimed responsibility for the attacks in the name of a group linked to al-Qa'ida and threatened more bloodshed unless Spain withdraws its troops from Iraq and Afghanistan in a week. The government says the tape was recorded 27 March.

The men on the tape said they spoke in the name of "the Al Mufti Brigades and Ansar al-Qa'ida". Part of their speech alludes to Socialist leader Jose Luis Rodriguez Zapatero, due to take over as prime minister on Friday. "Your new ruler has begun his mandate with more fighting against Muslims and sending more crusade troops to Afghanistan," according to the ministry's text. In another newly released sentence, the man seen reading on the tape says: "We will treat you brutally. We will kill you. We will you bring war to your homes, and you will not be able to sleep at night."

Since the 11 March attacks, more than 30 suspects have been taken in for questioning. Three were arrested yesterday bringing the total in custody to 24. Eighteen people, 14 of them Moroccan, have been charged in connection with the bombings. Six have been charged with mass murder.

Though the alleged ringleader - one of the seven who blew themselves up - is a Tunisian by the name of Serhane Ben Abdelmajid Fakhet, most are Moroccans who have lived in Spain for years, running local businesses and blending into Madrileño society.

Investigations now point in several directions, suggesting links with radical Islamic groups in countries including Britain, Iraq, Turkey and Norway. Sunday's edition of the Spanish newspaper El Pais, reported that the suicide bombers called a British number before setting off their lethal explosives.

In Norway - officers are tracking two Norwegian telephone numbers possibly linked to the Spanish group and suspect some level of financing from Oslo, according to a source close to the investigations. Whatever the international links, the attacks themselves were a simple affair that could be replicated elsewhere, Spanish investigators say.

In late February, three or four Moroccans drove a stolen car from Madrid to northern Spain and, paying in cash and hashish, acquired all or most of the dynamite they used on 11 March and for use in further attacks. In the strict world of Spanish explosives regulation where news of robbery from a mine typically results in heavy fines and costly security measures, the theft - facilitated by two Spaniards with previous convictions for trading in dynamite - was not reported.

At about the same time, Jamal Zougam, a 31-year-old Moroccan whose Western looks earned him the nickname "el blancon" (whitey) who ran a phone repair shop with two partners in Madrid's immigrant Lavapies quarter, purchased one hundred pre-paid phoncards from two Indian traders in the city. On the eve of the attacks, investigators say that the terrorists spliced 13 phones and phone cards into simple bomb concoctions.

Gathered in a squalid shack on an isolated plot of land outside Madrid, they assembled the dynamite parcels, spiked them with shrapnel and linked the detonators of each bomb to a mobile phone whose alarm settings were to trigger the blasts.

"It's an easy thing to do. You don't need to be a rocket scientist to make that sort of a bomb," said a Basque explosives expert.

The following morning, several of the men drove to two train stations, deposited the bombs in sports bags on four trains and stepped off, unhindered, before the blasts. Between 7.36 and 7.39 in the morning, ten of the bombs exploded, mangling ten train compartments. Police later detonated two bombs in controlled explosions.

"Any terrorist attack needs a good dose of luck to succeed," said Brynjar Lia, who heads a research project into radical Islamic websites for the Norwegian Defence Research Establishment in Oslo.

Months earlier, Mr. Lia had read and dismissed an internet document calling for attacks on Spain as an empty threat. " Jihadi Iraq, Hopes and Dangers," posted on the Global Islamic Media website in early December 2003, identified Spain as the weakest link in the Iraq war coalition. Verging on the prophetic, it called for a series of "painful strikes" against Spanish forces, which should coincide with the Spanish elections to topple Spain's pro-Bush administration and bring in a Socialist administration that would withdraw Spanish troops from Iraq and set off a domino effect.

Mr Lia, whose department has since issued a statement suggesting the Madrid attacks may have been inspired by the document, did not pay much attention to the document. "I told my wife about it and a friend too, but I didn't think it was worth alerting the intelligence service.

"You can't worry about every single threat you read on the internet," he said. In Spain itself, investigators were unaware of such calculations on the internet. "We never thought they would strike here," said a Spanish investigator. "Islamic radicals have always considered Spain a country of fellow believers. To attack here would be like soiling their own nest." So confident were the terrorists of their failsafe plot that they did not flee Madrid but returned to their workplaces in Spain.

Were it not for a single unexploded bomb whose phone card had not been activated, and which yielded crucial clues to the attacks, anti-terrorism officers say they would still be at the beginning stages of the investigation.

A decentralised brand of al-Qa'ida, coupled with websites that promote jihad, help to spread Osama bin Laden's ideology to local groups operating independently, Mr. Lia said in Oslo.

"Three years after the destruction of training camps in Afghanistan, al-Qa'ida is very capable. It has turned from a group into a movement, an idea that everyone wants to be a part of. That is the danger."