The powerful Casalesi Camorra clan is believed to have been behind the massacre at the Italian town of Castelvolturno, in which six African immigrants including three Ghanaians were slaughtered.
Police reports said the incident began with the shooting of an amusement arcade's 53-year-old Italian owner, known to have had links with the Casalesi.
Twenty minutes later, in another part of town, the six immigrants were mown down in a 120-round hail of fire from semi-automatic pistols and Kalashnikovs.
Three Ghanaians, two Liberians and a Togo national were shot dead at an ethnic clothing shop where local residents often brought clothes for minor adjustments.
A third Liberian died in hospital the morning of the following day. One suspect, 29-year-old Alfonso Cesarano, was arrested on Monday in connection with the murders and police are seeking two fugitives. Police said the murders were drug-related but also ''a signal'' that the Casalesi were still strong in the area despite a raft of recent arrests.
The Casalesi clan is one of the most feared Camorra outfits. Its criminal empire was exposed in Roberto Saviano's worldwide bestseller Gomorra, now also a film that won the second prize at Cannes this year.
La Russa also said Monday that the deployment of 3,000 troops in major Italian cities will be extended for another six months ''in light of the great success'' of the initiative - part of a wider government crackdown on crime.
The soldiers were sent in August to join police on patrols of nine cities and to guard sensitive sites such as embassies, government buildings and immigration holding centres across the country for a provisional six-month period new task force of 500 soldiers who will be deployed in cases of ''criminal emergency'' in response to a recent wave of Mafia crime.
Defence Minister Ignazio La Russa said ''the majority'' of the troops would be sent to help fight the Neapolitan Mafia in a bloody fief north of Naples following the worst ever Camorra massacre last week.
The soldiers will flank the 400 extra policemen sent to the province of Caserta on Monday to beef up protection after a string of Mafia murders this year which culminated in the shooting of six West African immigrants and an Italian on Thursday.
Defence Minister Ignazio La Russa stressed that the 500 troops will be in addition to the 3,000 soldiers deployed alongside police in major Italian cities this summer.'' The troops (in Caserta) could be deployed for three months and (perform) the functions of manning check points,'' La Russa explained.
Italy's anti-mafia prosecutor, Piero Grasso, hailed the decision. ''We need to put into play everything that can be useful in resolving the problem,'' he said.
But the opposition Democratic Party's deputy House whip, Marina Sereni, described the decision as ''belated'' following Thursday's massacre.
''This government continues to use cosmetic stunts for dealing with crime such as deploying soldiers in the big cities, but it has abandoned whole areas of our country to organised crime,'' Sereni said.
This will be the second time since the 1990s that the army has been sent in to combat Mafia crime in southern Italy.
Some 150,000 soldiers were sent to Sicily in 1992 following the murder of anti-Mafia judges Giovanni Falcone and Paolo Borsellino.
They stayed on the southern island until 1998 in an operation dubbed Sicilian Vespers. The Italian government weighed sending the army to stop a turf war in Naples itself two years ago, but eventually decided against it.