Police in Germany and Italy have arrested four members of feuding Italian families linked to mafia deaths in the German city of Duisburg.
Police raided San Luca in August, arresting more than 30 people
Six Italian men from the Calabrian Mafia, the 'Ndrangheta, were shot dead outside a pizza restaurant in August.
Two of the arrests were made in Germany's North-Rhine Westphalia region and two in Calabria, southern Italy. Police are looking for a fifth suspect.
The authorities believe the killings were part of a long-running vendetta.
Two of the suspects were arrested in the small Italian town of San Luca, the focal point of a bitter feud between rival clans among the 'Ndrangheta.
The town has been blighted by mafia killings for more than a decade.
The other two suspects were arrested in North-Rhine Westphalia, where Duisberg is situated, after a tip-off from Italian police.
The four are not believed to have been directly involved in the murders, Italian media say.
The murders took place on 15 August after a birthday party celebration.
The 'Ndrangheta, which is notorious for vendettas, is believed by police to control cocaine trafficking in many parts of Europe.
The clan feud in San Luca, a town of about 4,500 at the southern tip of Italy, dates back to an egg-throwing incident in 1991.
A fight broke out which left two young men dead and another two injured.