A group of Calabrian mafia assassins beat a rival with a spade and fed him alive to pigs, Italian police said after rounding up 20 people for various mob crimes including five murders.

The murder probably took place in March 2012 when Francesco Raccosta disappeared, but his body has never been found, the court in the southern city of Reggio Calabria said in a statement.

Investigators arrested one of Raccosta's suspected assassins after they captured him bragging about the hit in a telephone wiretap.

"It was such a pleasure to hear him scream," the suspect said. "In my opinion, there's nothing left of him ... This pig can really eat!"

The murder was one of five carried out in retaliation for the killing of boss Domenico Bonarrigo, who was shot three times while driving his car 11 days earlier, according to investigators.

The murders were part of a mob war between rival factions of the 'Ndrangheta, as the Calabrian mafia is known, for control of the criminal activities in the territory near the town of Oppido Mamertina, on the "toe" of the Italian boot.

Thanks to its dominant role in bringing cocaine into Italy and Europe, the loose-knit Calabrian mob, made up of more than 100 different clans, has eclipsed the economic power of the Sicilian mafia, Cosa Nostra.