Last Wednesday evening, the most famous face of Rome’s criminal underworld was sitting on a bench in the Parco degli Acquedotti – the “park of the aqueducts” – in the south-east of the city. Fabrizio Piscitelli, 53, was well-known because, for almost 30 years, he had been the undisputed boss of Italy’s toughest ultra gang, Lazio’s Irriducibili (“the Irreducibles” or “Die Hards”). He was nicknamed “Diabolik”, after a cartoon thief and assassin.

Shortly before 7pm, a man dressed as a jogger – wearing a cap and neck-scarf – ran past the bench and fired a 7.65 calibre pistol into Piscitelli’s left ear. He died almost instantly, sliding off the bench as the murderer ran off. It had all the hallmarks of a professional hit.

The murder brought to a close one of the most incredible careers in the history of Lazio’s ultras. The club’s fanbase has always been very politicised: during Italy’s “years of lead” (its extremist terrorism) in the 1970s, it was very common to see, among the white-and-sky-blue colours of Lazio supporters, many of Benito Mussolini’s symbols. It was an era in which Lazio ultras became both victims and perpetrators of political assassinations.

That was the turbulent decade in which Piscitelli first went to the stadium. But it was a period of sporting decline: the team’s glorious 1974 scudetto (meaning it had won the Serie A championship) was fading from view, and soon match-fixing scandals would relegate the team to Serie B and, almost, to C.

Piscitelli wasn’t overly interested in football, though. By the time he was in his teens, the real match was with rival ultras. He was a street-fighter. “For the good of Lazio,” he once said, “we were looking to injure people on the other side, we wanted to go onto the terraces and kill them.” Fighting, he said, made him “feel alive in a world of the dead”.

By the mid-1980s, Lazio’s predominant firm, the Eagles, seemed too sedate for Piscitelli and the other teenagers who were hanging out with a graphic designer called Grinta (“Grit”). In 1987, Grinta and his tearaways founded a new crew, the Irriducibili, using as their symbol a bowler-hatted character called Mr Enrich swinging a kick. They fought the Eagles for terrace supremacy, easily getting to the centre of the curva (the curved terrace) by the tactic of being willing to use far more violence than their rivals.

It was fortunate timing. Lazio enjoyed a revival in the 1990s. The club signed world-class players like Beppe Signori and Paul Gascoigne. It was taken over by a wealthy entrepreneur, Sergio Cragnotti. Guided by the Swedish manager, Sven-Göran Eriksson, Lazio won its second scudetto as well as a Uefa Cup and two Italian cup finals.

Suddenly there was a lot of money in both football and, specifically, in Lazio. Ultra firms had always produced stickers, scarves, badges, fanzines and shirts to subsidise their choreographies, rent and travel, but the Irriducibili took it to another level. They rented warehouses, opened franchises and became experts at using the stadium to publicise their political, and sartorial, pose. Their slogans and stunts always made the papers, and often the television. Seeing the amount of money to be made, Piscitelli deposed Grinta as the leader of the Irriducibili and turned the cottage industry into a business empire called Original Fans.

Facebook Twitter Pinterest Fabrizio Piscitelli, aka Diabolik. Photograph: Il Tempo.it

At its peak, Original Fans had 12 outlets. The turnover was largely cash-in-hand so precise figures are hard to come by, but Piscitelli became a millionaire. (An estate of €2.3m was confiscated from him in 2016). The deeply offensive extremism of the Irriducibili helped brand the Original Fans label. Swastikas, Roman salutes, antisemitism, hanging mannequins from bridges, plastering Anne Frank stickers as insults, singing the national anthem during silences for drowned migrants … the Irriducibili were always in the news and began attracting thousands of recruits from far-right parties like Forza Nuova. All adherents, of course, had to pay a subscription and purchase the right clobber. “If Piscitelli weren’t a gangster,” a Lazio supporter told me once outside the Stadio Olimpico, “he could have been a CEO.”

Piscitelli was charismatic: he could be pally and charming, and when in his company you felt you were at the court of a cheeky king. But he could turn nasty in a flash. An acquaintance of his remembers: “He would suddenly say things like ‘let’s fucking shoot him’ and you didn’t know if he was serious or kidding.”

At the height of his power, Piscitelli could get anyone he wanted into the stadium (even, very showily, himself despite one of his many stadium bans). Another Lazio ultra (scornful of the incessant fascism of the Irriducibili) says that for many years “Piscitelli could do whatever he wanted”. A police union representative once complained, on TV, that the capo-ultrà was introduced into certain police corridors that were closed even to him, the official rep.

Income and connections made the Irriducibili very powerful. Toffolo, another leader of the group, once boasted of being a trade union leader: “I represent 15,000 people,” he said. There was absolute unity in the ranks: four huge speakers were installed in the curva nord so that everyone was forced to follow the leader. Spontaneity was punished; dress codes imposed. “No one would ever dare be arrogant here,” one of the leaders once told me, “because we’re a military organisation.” The group organised riots to stop tax debts being imposed on Lazio by the Italian government. It boycotted newspapers. It even attempted to take over Lazio itself, financed by money from organised crime and using Lazio’s Italo-Welsh legend, Giorgio Chinaglia, as a frontman.

Piscitelli was taking increasing risks. He had moved from merchandising into drug dealing, using his connections to the Neapolitan mob, the Camorra. His batteria (turf) was the Ponte Milvio suburb just north of the Stadio Olimpico. By then the violence had moved far beyond terrace fisticuffs: Toffolo was twice knee-capped by unknowns, and the leg of one Irriducibili, having been chainsawn off, was found in a tributary to the river Tiber (his body was never found). Piscitelli was accused of handling hundreds of kilos of narcotics and was eventually arrested in 2015 after police followed a pizza delivery boy to a remote warehouse. Piscitelli’s hideout contained axes, swords, truncheons, a pistol and phone-jammers.

He was first imprisoned and then placed under house arrest. His villas were confiscated. Other ultra groups, such as Hit Firm, were snapping at his heels. With years of court appearances pending, Piscitelli tried to make a comeback. He made peace with Claudio Lotito, the Lazio chairman against whom he had plotted for so long. There were more stunts, like Roman salutes honouring Mussolini in Milan this spring, and a comuniqué in which women were banned from the front 10 rows. It all generated news and Piscitelli openly spoke about his hope for a return to the “years of lead”.

But by then his power, and health, were on the wane. Ironically for a terrace in which the far-right fans forbid recreational drug-use, Piscitelli was, for much of his life, an avid drugs user. In a 2002 BBC documentary about Lazio’s ultras, he happily rolled a joint while simultaneously driving his car around the stadium. That drugs use didn’t add to his emotional stability. One psychiatric report (admittedly prepared by his defence team, in the hope of avoiding a custodial sentence) portrayed a man who was prone to frequent bouts of psychosis, paranoia and delusion. . Perhaps, in the end, his criminal contacts simply thought it was safer to have him out of the way.

The Irriducibili is still intimidating. No Lazio ultra will go on the record to speak ill of the deceased. But one lifelong fan summed up, more bluntly than most, what many Laziali said in private last week: “Piscitelli ruined the image of Lazio in the world. Lazio now implies racism, fascism and collusion with the Camorra. His was a rabble of criminals.” Diabolik, it’s clear, took fandom far beyond the football.

Tobias Jones’s new book, Ultra, is published on 19 September by Head of Zeus

Who are the ultras?

Facebook Twitter Pinterest SS Lazio ultras clash with riot police at the end of the Serie A match between SS Lazio and AS Roma in 2015. Photograph: Stefano Montesi/Getty

• In the late 60s and early 70s, teenage football fans rebelled against Italy’s sedate supporters’ clubs and went to stand, and sing, behind the goal. They’ve been compared to punks and Hells Angels.

• The word “ultra” implies “extreme”, “beyond” or “other”.

• At its foundation, the movement was largely far-left, with names inspired by global partisan struggles. Petty criminals and political extremists were drawn to the terraces’ carnival atmosphere and the huge customer base. Most ultra groups are now fascist in inspiration and many have overlapped with organised crime.

• Ultras are comparable to, but different from, British football hooligans. They relish drinking and fighting, but are much more hierarchical and disciplined, with a sober strategic analysis of the group’s sporting, and economic, interests.

• Despite their reputation, there are ultra groups that are inspiring, charitable and inclusive.