A "super-witness" who was due to testify on the links between politicians and mafia mobsters in Naples was gunned down in the street yesterday - the fourth victim in a month of shootings directed against witnesses who turn state's evidence.

The killing of Michele Orsi, the 47-year-old boss of a waste disposal firm, highlighted the Italian state's inability to protect people prepared to give evidence against organised crime.

As security officials yesterday held crisis talks, Orsi's murder gave a new and sinister twist to the Naples garbage crisis, where rubbish is still piled high on streets and roads in Campania, the region that includes the city. Since the emergency began last December one of the worst-affected provinces has been Caserta, where Orsi was shot dead in a bar in the town of Casal di Principe yesterday afternoon.

The Carabinieri, the military police, said yesterday the killing was impossible to reconstruct because no one would admit to having seen it. However, after a search for bullets and casings, they concluded that at least 18 shots were fired from two 9mm-calibre automatics. Orsi was hit twice in the chest and once in the head, suggesting that, in classic mafia style, he was given a "coup de grace" by one of the killers as he lay dying.

Casal di Principe is the home town of the author Roberto Saviano and features prominently in his best-selling book, Gomorrah. Saviano, who lives under round-the-clock protection because of death threats, said yesterday Orsi was a "leading entrepreneur in the waste sector who did millions of euros' worth of business with the [mafia] clans". Orsi's lawyer, however, described him as a victim whose company had been paying at least €15,000 a month to the Camorra, the mafia of Naples and Campania.

The murdered businessman was to have given evidence on Thursday in a trial in which the defendants include a prominent member of Silvio Berlusconi's governing Freedom People alliance.

Franco Roberti, the chief anti-mafia prosecutor of Naples, said: "A formidable opportunity to strike at the clans has been lost." He told the daily La Repubblica paper that Orsi "had decided to talk [and] denounce all the bonds that link politics to the Camorra. His words would have angered many people. Too many of them had an interest in taking him out."

Roberti said the only effective way to protect witnesses was to move them out of territory controlled by the mob, and Orsi had not applied for inclusion in a programme that would have enabled that to happen. However, the dead man's lawyer said: "Orsi was frightened. He came to my office every day because it was the only place he felt safe."

Camorra gangs are themselves leading players in the waste disposal sector - illegally dumping toxic waste, usually trucked down from the more industrialised north of Italy.

Their presence is also a key reason why people in Campania are so opposed to the construction of incinerators that would provide them with a long-term solution to the region's waste problems. They fear the facilities would come under the control of the Camorra and be used to burn toxic waste.

Orsi's death also appeared to form part of a killing spree intended to stem the flow of secrets of the mob clans operating in and around Casal di Principe. It began on May 2 when Umberto Bidognetti, the father of a mobster turned state's witness, was shot dead at nearby Castelvolturno.

Two weeks later hitmen killed a businessman who gave vital evidence against racketeers in a trial in 2001. Then, on Friday night, mobsters disguised as police officers demanded to be let into a flat owned by relatives of another state witness, Anna Carrino. The former partner of a "godfather" her testimony has led to the arrest of several of his henchmen. Her niece opened the door and was shot in the stomach. She is expected to live.

Backstory

Campania has been the scene of intermittent rubbish crises for 14 years. The latest started in December 2007, when all of the region's landfill sites were full. The sight of piles of garbage on the streets of Naples was for many symptomatic of the country's apparent inability to reform itself. It was one reason for the fall of the government of Romano Prodi in April. On May 21 Silvio Berlusconi's new government approved the opening of eight dumps to deal with the immediate problem and the building of four incinerators as a longer-term solution. Protests by residents against the opening of dumps continue, however. On Sunday 10,000 protesters held a rally at one site.