They dragged him from the car and decapitated him in front of his family. Before driving away they dumped the severed head in the lap of the colonel's nine-year-old son.
The incident, which took place in January, is typical of the 50 or so killings a week by sympathisers of the Islamic Salvation Front (FIS) and even more extreme groups, such as the Armed Islamic Group (GIA). Most victims die from shooting, but other methods, such as castration and throat- cutting, are common
With every death, apprehension mounts across the Mediterranean. France, the colonial power in Algeria for 130 years until 1962, knows it will bear the brunt if, as seems inevitable, the conflict spills over Algeria's borders.
The 4,000 Algerian victims so far have been intellectuals, journalists, government officials, members of the police and military. The latter have included young conscripts - one was taken home so his wife could watch his throat being cut. Even teenage girls have been shot dead for not wearing Muslim headscarves. And 34 foreigners have been murdered since a campaign to drive foreign residents out began in September last year.
The crisis, in a country beset by debt and struggling to meet International Monetary Fund targets, became acute in 1991, when the government cancelled the second round of elections after the FIS emerged as the winner in the first round.
At that time, senior officials in Paris said privately that they believed the Algerian government had two years in which to bring the country under control. That effort has clearly failed. Now officials say Algeria may be only weeks away from full-scale civil war. France, although it is said to be trying to persuade its European Union partners to help Algeria with an aid package, seems to have lost all hope for the government of General Lamine Zeroual.
Last month Paris urged all French nationals to leave Algeria after two Frenchmen, a father and son, were killed in Algiers, bringing the number of French deaths to eight.
Thousands of Algerians have started arriving in France, adding to the 1 million people of Algerian extraction already residing here. Estimates of the numbers of Algerians with dual nationality still living in North Africa vary, but they start at 25,000. All have automatic right of residence in France.
Last year, according to official figures, 1,098 Algerian nationals asked for political asylum because they believed their lives were in danger, up from 144 in 1990.
A large influx of refugees would exacerbate social and racial tensions in a country which already has 3.3 million unemployed. The authorities are said to be discreetly preparing camps on disused military bases in anticipation of a rush.
'What people here don't realise,' said an Algerian shopkeeper in Paris, 'is that the bulk of the Algerian population is under 20. For every adult who comes, there'll be 14 behind, enough to fill a holiday camp.'
Some talk of 'boat people' and recall the sight of an Albanian ship, crammed with thousands of refugees, trying to tie up in the Italian port of Brindisi a couple of years ago.
A worse fear is that the violence will be imported, too. This would lead first to violence between sections of the Algerian community in France and then, if the fundamentalists decided to expand their war, to French targets.
Last week police said arms, ammunition and false documents had been found in the homes of two Algerians in Lille and the Paris suburbs respectively after they had been detained for heroin trafficking.
The arrest of Chaid Eddour, 39, and Ahmed Seba, a 28-year-old French national, seemed to confirm that the FIS was using the drugs trade to help finance its activities.
The investigation was handed to Jean-Louis Bruguiere, the examining magistrate in charge of the section of the prosecutor's office which co-ordinates the fight against terrorism. In the absence of much official information, a number of leaks have given an insight into French concerns.
Investigators believe the two detainees were just a tiny part of a terrorist logistics network which has other arms caches in France.
Among the arms found last month was an Israeli Galil rifle - a gun which Israel has never exported. Therefore, the sources said, it must have been a captured weapon. They suggest it could have come from south Lebanon and, if so, was probably delivered to Algerian fundamentalists by Iranians.
Such talk triggers very bad memories. In 1986, 13 people were killed and many maimed in a series of bomb attacks concentrated on Paris by a group calling for the liberation of three Middle Eastern prisoners in French jails.
That network was broken up when one of its members turned himself in to the Direction de Surveillance du Territoire (DST), the French counter-espionage service. The informer gave the authorities information which led to the discovery of an impressive logistics operation with arms caches and the potential to unleash a new campaign of violence. Its members were mainly North Africans, some with French nationality, who had lived apparently peacefully for years in France, running cafes and shops or driving taxis.
The subsequent trial heard that Iranian groups had armed and trained the members of the French-based network for an offensive in Europe.
Over the past few months, French and German officials, anticipating Germany's presidency of the EU starting on 1 July, followed by France's presidency six months later, have been co-ordinating their policies to give the EU at least 12 months of continuity.
According to diplomatic sources, France became frustrated because of Germany's wish to give Eastern Europe priority, while the French believed Algeria needed more urgent attention. 'Germany replied that Algeria was a neighbour, but that East Europe was family,' one source said.
Despite the doomsday scenarios in French official circles, the crisis in Algeria and its possible consequences for France have not yet fully grabbed the public imagination. Last week, the weekly Le Point, under the headline 'L'Horreur', gave a graphic account of atrocities in Algeria. The situation, wrote Michel Colomes, the magazine's foreign editor, had not attracted enough interest because 'in our civilisation of electronic media, nothing exists without an image and television channels cannot, because of censorship or physical threats, provide their dose of daily violence to the evening news bulletins'.
Reports written by Algerian journalists for Le Point told of the 'Ninja Turtles', the black- masked government security men who ride shotgun on buses and try to keep a semblance of control in the cities - a control which evaporates at night.
In some parts of the countryside, the fundamentalists are more or less in charge and have forced the closure of tax offices by threatening government employees and forcing locals to pay only 'Islamic' taxes to the fundamentalist groups - depriving an already bankrupt state of its last cash resources.