The Big Question: Has the Italian mafia spread its tentacles throughout Europe?

Why are we asking this question now?

Six Italian men who worked at a pizzeria in the north German industrial city of Duisburg were shot dead outside their restaurant at 2 o'clock on Wednesday morning. They were affiliated to one branch of the 'ndrangheta, the criminal organisation based in Calabria, at the toe of the Italian boot. Investigators believe their killers belonged to another clan in the same organisation. The two clans, which come from the same village, have been engaged in a bloody feud since 1991.

Why where they killed?

On Christmas Eve last year, Maria Strangio Nirta, the wife of the godfather Giovanni Nirta, was shot dead on her doorstep. Police believe that the principal target in yesterday's massacre was a man called Marco Marmo, 25, who was under investigation by the police for alleged involvement in that murder. By committing the massacre on 15 August, the Feast of the Assumption, a religious holiday almost as important in Italy as Christmas, they enjoyed their revenge dish both cold and symmetrical.

Do atrocities of this sort happen frequently?

Yes, but not outside Italy. Italian experts say it is unprecedented for the 'ndrangheta to pursue a blood feud beyond the borders of Italy. The feud between the two families, the Strangio-Nirta and the Pelle-Romano, has been under way for 16 years, but till now all the attacks have been confined to the village of San Luca, where the two families are based.

Is the 'ndrangheta the same as the Sicilian Mafia?

No. The two organisations are only separated by a few kilometres and the Strait of Messina, but while Cosa Nostra is a unified organisation with a capo di capi ("boss of bosses") and fiercely imposed collective discipline, the 'ndrangheta functions differently. "The various clans are autonomous," says the Mafia historian John Dickie of the Calabrian organisation. "They have held regular meetings since the 19th century to settle differences, but they are far more anarchic than the Sicilian Mafia, much more like families with guns. They have no mechanism for imposing collective discipline."

How did it come by this name?

One explanation is that it derives from a Greek word for virility or courage. There is also an old word for this part of Italy that might be behind the term.

Why haven't we heard much of them before?

Until the day before yesterday they were the soul of discretion, "invisible", as one Italian put it, "like the dark side of the moon". But also because in the popular imagination, especially outside Italy, the Mafia is so closely identified with the island of Sicily. Despite the anarchic tendencies mentioned above, the 'ndrangheta have grown rapidly richer over the last couple of decades without drawing attention to themselves in the theatrically violent manner of Cosa Nostra, which provoked unprecedented state retaliation 15 years ago after a string of high-profile assassinations.

What are they doing in Germany?

Running restaurants such as Da Bruno, the scene of Wednesday's atrocity. (One of the restaurant's owners, a Calabrian like all the victims, said the following day, "I curse the land of my birth.") Italians from the impoverished south emigrated in huge numbers to the Ruhr coalfield and other industrial areas of Germany, Belgium, Holland and France after the war to work. They sank roots in the area and hundreds of Calabrian families still live in Duisburg today. And quietly but persistently the criminal gangs followed them, battening on their co-nationals like lice, communicating in dialect, shaking down Italian businesses for protection money just like they did back home.

Is protection money still their main source of income?

By no means. Calabria has become Europe's most important source of illegal cocaine, with 80 per cent of the trade supposedly passing through the Calabrian port of Gioia Tauro. Italian secret services believe that thanks to cocaine and heroin and other booming businesses such as arms trafficking, the Calabrians are now the richest and most powerful of the criminal syndicates, outstripping both Cosa Nostra and the Camorra network based in Naples.

Their international business brings in a turnover of some €40bn per year, equivalent to 3.5 per cent of Italy's gross domestic product. This is where the foreign friends come in handy: drug money is meaningless without an outlet in the legal economy, and the Calabrians have been working hard to penetrate the socio-economic fabric of the cities where their fellow-countrymen have settled.

Starting as a marginal, parasitic, intimidatory presence they use their vast wealth to muscle into real estate, hotel and restaurant businesses, all of which facilitate the laundering of drug money. It has been helped in this endeavour by the lack of pubic awareness of the 'ndrangheta's existence. As a report by the Italian secret services to parliament spelled out earlier this year: "It is precisely the low visibility of the 'ndrangheta, and their lack of impact in the media, that has enabled them to stay out of reach of the authorities, because they do not set off alarm bells. In this way the Mafia power systems seek to infiltrate and silently consolidate their territorial and social denomination."

Where else are they strong?

They have close ties with gangs in the Balkans, especially the Albanians, as well as in other parts of Eastern Europe. They have cordial business relations with criminal gangs in Turkey, from which they import heroin, the South American gangs from which they source cocaine, and are strong in the Italian immigrant communities in Australia and Canada. They are also flourishing in in northern Italy.

Everywhere they operate they are turning increasingly white collar. Drug money fuels their growth and expansion, but it dictates that they must muscle into legitimate business so they can launder the proceeds. For example their involvement in public works contracts in southern Italy, a very traditional Mafia speciality, now extends beyond providing dummy sub-contractors and a pliable workforce: now, say the secret services: "They also aim to infiltrate and occupy the administrative structure in the road-building programme, giving them the power of direct intervention and management."

And their ambition spreads inexorably to the more prosperous Italian north. The mayor of a town near Milan who recently banned Calabrian firms from bidding for public building projects in his area received a Happy Easter card containing a bullet, and had his car set on fire.

Was the Assumption Day Massacre a good business move?

Terrible: in one brief orgy of violence, decades of stealthy infiltration by the 'ndrangheta has been undone. Most Germans had never heard of them before: Germany has been profoundly shaken by the attack and can be expected to give Mafia-related businesses a hard time.

What can to be done to stop them?

San Luca has been flooded with Italian police since the killings. That won't do any good: the killers waited more than six months to take revenge, and the next act could be an equally long time coming. Further afield, anti-terrorism legislation that makes the movements of funds far more difficult may cramp the style of all the Mafia clans. But in places like Duisburg they are so well entrenched that they will be hard to winkle out.