Thousands of people have paid homage to a mafia boss who died in Australia after successfully avoiding prosecution for his alleged role in the murder of anti-drugs campaigner Donald Mackay in 1977.

A funeral for 82-year-old Italian mobster Antonio "Tony" Sergi was held at the Sacred Heart Catholic Church in Griffith, Riverina region, on 3 November.

Leonard Cohen's Hallelujah was played as Sergi's casket, adorned with white lilies and roses, was carried out of the church, the Sydney Morning Herald reported.

Sergi was born in Plati, Calabria, on 29 October 1935. He was a member of the Italian mafia syndicate known as 'Ndrangheta, which is today the most powerful Italian mafia.

Sergi moved to Australia in 1950s and became a well-known winery proprietor in Riverina.

He came to the attention of the authorities after a Royal Commission into drug trafficking (1977-1979) identified him as a major figure in the illicit trade. He was referred to as "the operator" in the Griffith marijuana industry.

Sergi was alleged to be behind Mackay's murder in 1977.

The corpse of the activist, who had tried to run as a Liberal candidate in 1974, has never been found. His disappearance remains one of the most high-profile unresolved crimes in Australia's recent history.

Sergi, known locally as "the don of dons", was alleged to have planned the murder after Mackay was revealed as the police informer who exposed a large marijuana crop being cultivated in Coleambally, ABC News reported.

Clive Small, former New South Wales (NSW) assistant police commissioner who investigated the murder, told the news site a dozen local mafiosa had "pre-arranged alibis".

"There were a number of people ... Tony Sergi, Bob Trimbole and a number of others, who had agreed that the murder of Donald Mackay was to be carried out,"he said.

"In the 1970s, Tony Sergi, Bob Trimbole and a number of others played a very significant and high-profile role in the introduction of the Calabrian mafia to the cannabis trade,"

"They really had an impact on that organisation in terms of the profits it was making, in terms of its growth and its connections and right through to its existence today," Small continued.

He previously told the Daily Mail there are at least 31 Calabrian mafia families that controlled 60% of Australia's drug trade.

"[To this day] the 31 Calabrian mafia families across Australia report to five families in Calabria, which are really nine families integrated by marriage," he said at the time.

What is the N'drangheta?

In recent years, 'Ndrangheta has become Italy's most powerful and feared mafia group. Part of its criminal success is down to its secretive nature. As clans are founded on strict blood ties, members rarely turn informer, making detectives' work harder.

'Ndrangheta is widely regarded as the group that has filled the void left by Sicilian mafia Cosa Nostra on the international drug trafficking stage, gaining the crown of Europe's biggest drug cartel.

A series of recent investigations has shown how its clans have become the favourite business partners for US mafia families, previously tied to the Sicilian mob.

Besides drug trafficking, 'Ndrangheta gangs are involved in several other illicit activities, except for prostitution, according to Enzo Ciconte, a professor of organised crime history at Rome University.

Italian Mafia Map
A map of Italy's four mafia groups and their regions of origin IBTimes UK