A two-year BBC investigation into Black Axe - a Nigerian student fraternity which evolved into a dreaded mafia-group has unearthed new evidence of infiltration of politics, and a scamming and killing operation spanning the globe.

Warning: Contains detailed graphic accounts of violence

During quiet moments, after he has finished lecturing for the day, Dr John Stone has flashbacks. It's not the blood or the sound of the gunshots that haunt him. It's the begging. The way people beg for mercy when they die. Begging him. Begging God.

"It's so painful," he says, shaking his head with a shudder. "The families of the dead, they will curse you. A curse will be upon your life."

Dr Stone teaches political science at the University of Benin, in southern Nigeria. But for decades he was a senior member of Black Axe - a Nigerian mafia-style gang tied to human trafficking, internet fraud and murder. Locally, Black Axe are referred to as a "cult," a nod to their secret initiation rituals and the intense loyalty of their members. They are also infamous for extreme violence. Images of those who cross their path - dead bodies mutilated or showing signs of torture - regularly surface on Nigerian social media.

Dr Stone admits he took part in atrocities during his years as an "Axeman". At one point during our interview, recalling the most efficient means of killing, he leaned forward, squeezed his fingers into the shape of a gun and pushed them to the forehead of our producer. In Benin City, he was known as "a butcher".

The horror of these years has scarred him. Today, Dr Stone is remorseful for his past and a vocal critic of the gang he once served. He is one of a dozen Black Axe sources who have decided to break their oaths of silence and reveal their secrets to the BBC, speaking to international media for the first time.

For two years BBC Africa Eye has been investigating Black Axe, building a network of whistle-blowers, and uncovering several thousand secret documents - leaked from the gang's private communications. The findings suggest that over the past decade, Black Axe has become one of the most far-reaching and dangerous organised crime groups in the world.

In Africa, Europe, Asia and North America, Axemen are in our midst. You may even have an email from them in your inbox.

Our investigation began with a death threat - a spidery, hand-written letter, delivered to a BBC journalist in 2018. It was dropped by a motorbike rider on to the windscreen of the reporter's car. Weeks earlier, the journalist had been digging into the illegal opioid trade in Nigeria and had met a number of Black Axe members face to face. Later, a second letter was handed to the man's family. Someone had been tracking him and had found his home.

Did the threat come from Black Axe? How powerful is this crime network, and who is behind it?

Our search for answers led us to a man who claimed he had hacked tens of thousands of secret Black Axe documents - a huge cache of private communications, from hundreds of suspected members. The messages, which span 2009 to 2019, include communications about murder and drug smuggling. Emails detail elaborate and lucrative internet fraud. Messages plan global expansion. It was a mosaic of Black Axe criminal activity spanning four continents.

The source of the hack claims Black Axe are desperate to kill him. He would not reveal his real name, instead he used a pseudonym - Uche Tobias.

"A manhunt will befall you," reads one death threat, sent to Tobias online. "The AXE will pierce through your skull… I will lick your blood and chew your eyes."

The BBC spent months analysing Tobias's documents. We were able to verify key sections of the data - confirming that individuals mentioned, and a number of the crimes committed in the documents, did take place. Much of the hacked material is too horrifying to publish. Axemen use secret forums - password-protected websites - to share photos of recent murders in internal chat groups. In one post labelled "Hit", a man lies splayed out on the floor of a small room. There are four gashes on his head. His white T-shirt is surrounded by a pool of his own blood. The imprint of a boot, stained red, marks his back.

Within Nigeria, Black Axe is fighting a war of supremacy with rival "cults" - similar criminal gangs with names like the Eiye, the Buccaneers, the Pirates and the Maphites. Messages the BBC have translated from West African Pidgin show Axemen keeping track of how many rivals they have murdered, tallying up the figures like a football score in each region.

"Score is presently 15-2, the war is Benin," reads one post. "Hit in Anambra state. Score is Aye [Axemen] 4 and Buccaneers 2," reads another.

But internet fraud, not murder, is the primary source of revenue for the gang. The documents given to the BBC include receipts, bank transfers and thousands of emails showing Black Axe members collaborating on online scams around the world. Members share "formats" - blueprints on how to conduct scams - with each other. Options include romance scams, inheritance scams, real estate scams and business email scams, in which the perpetrators create email accounts that appear to be those of the victim's lawyers, or accountants, in order to intercept payments.

These scams are not small-scale, conducted by a lone wolf on a laptop. They are collaborative, organised and extremely lucrative operations, sometimes involving dozens of individuals working together across continents.

Among the leaked emails, the BBC uncovered a case of a man in California who was targeted by a network of suspected Axemen in 2010, scamming him from Italy and Nigeria. The victim told us he was defrauded of $3m in total.

"The Bank that I was working with does not seem to exist???" the desperate victim exclaimed in an email to one of the conmen - the moment he realised his money was missing. "Can I make this any clearer??? The Bank in Switzerland seems to be fraudulent."

The emails show suspected Black Axe members adopting "catcher" names - fake names and identities - when scamming people, making use of forged or stolen passports. They refer to their victims as "mugu" or "maye," regional slang words for "idiots".

Black Axe's international cybercrime network is likely to be generating billions of dollars in revenue for their members. In 2017 Canadian authorities say they busted a money laundering scheme linked to the gang worth more than $5bn. Nobody knows how many similar Black Axe schemes are out there. The leaked documents show members communicating between Nigeria, the UK, Malaysia, the Gulf States, and a dozen other countries.

"It's spread all over the world," the source of the data hack told us. He says he's an anti-fraud investigator in his private life and began pursuing Black Axe after encountering a number of their scam victims.

"I would estimate there are upwards of 30,000 members," he says.

Black Axe's global expansion has been carefully constructed. The correspondence shows Axemen dividing geographic areas into "zones," and designating local "heads". Zonal heads collect "dues" - something akin to membership fees - from those in their jurisdictions, before sending the money back to leaders in their heartland in Nigeria's Benin City.

"It has spread throughout Europe and America, South America and Asia," says Tobias. "It is not a little club, this is a fantastically large criminal organisation."

Tobias's assessment is backed up by international law enforcement findings. According to the 2021 Organised Crime Index, based on analysis from 120 experts in Africa, Nigeria has the highest levels of organised crime on the continent - and these networks are expanding abroad.

In Italy, decades-old mafia laws are being revived to tackle the expansion of Black Axe, who are said to be overwhelming local crime networks. In April 2021, 30 suspected members were arrested in the country, charged with human trafficking, prostitution and internet fraud.

The US has taken a more aggressive approach. FBI operations against Black Axe were launched in November 2019 and September 2021, eventually charging more than 35 individuals with multi-million dollar internet fraud. Between September and December this year, the US Secret Service and Interpol launched an international operation to arrest a further nine suspected Black Axe members in South Africa.

"Cybercrime is a multi-trillion dollar industry, it's out of control," says Scott Augenbaum, a former FBI special agent and cyber-security expert.

He says he dealt with hundreds of Black Axe victims during his 30-year career in the bureau's cybercrime department, investigating fraud cases similar to those found in the leaked documents.

"I've seen lives destroyed, companies go out of business, life savings lost," he said. "It affects everyone."

As global as Black Axe's criminal empire maybe, its roots lie firmly in Nigeria. The group was founded 40 years ago in Benin City, Edo State.

Most Axemen are from this region, and this affiliation may have played a role in the group's international expansion. According to the UN commissioner for refugees, 70% of Nigerians who migrate abroad are from Edo State. Black Axe are reported to play a pivotal role trafficking those who travel illegally, moving them between their bases in Benin City, North Africa and Southern Italy.

In their homeland, male university undergraduates - aged between 16 and 23 - are Black Axe's primary recruits. The gang's secretive initiation process, known as "bamming," is notoriously brutal.

"I didn't know I was going to bam that day," writes one Axeman, detailing his experience in a post on a secret forum from 2016. He says he was led away from campus, thinking he was attending an exclusive party. He writes how he was taken to a forest, where a group of men were waiting for him. They stripped him and forced him to lie face down in the mud. Then they took turns whipping his skin raw with bamboo, beating him close to unconsciousness. Someone screamed they would rape his girlfriend, and when he had finished, he would rape her again.

"That was going to be the day I die," he writes.

But the agony eventually stopped. A series of rituals followed, including crawling through the legs of his tormentors - a tradition known as the "devil's passage" - before drinking blood from a cut in his thumb and chewing a kola nut, a caffeinated nut native to West Africa. To the echoes of songs and chants, he was then embraced by the men who had just tortured him. He had been reborn as what they call an "Aye Axeman."

There are many reasons people join Black Axe. Some recruits are forced, others volunteer. In Makoko, a vast slum built on wooden stilts above Lagos Lagoon, we interviewed a number of Axemen, some of whom said they had joined against their will. Their loyalty, nevertheless, was strong - cemented by the spiritual bond of the initiation process.

"We worship Korofo, the unseen God, and he has always guided us," the leader of the group told us, sitting in a small wooden building, surrounded by an entourage of Axemen. He said he was "proud" to be a member of Black Axe, despite saying he was forcibly recruited by a police officer. Another member claimed he joined after his father was killed by a rival gang. No matter how or why members join, many of them claim there are benefits.

"Secrecy, discipline and brotherhood," a cult member told us proudly during another interview in Lagos in April 2021, when we asked why he had joined Black Axe. He claimed he made good money through the group's criminal enterprises - better than he would earn working in a bank.

"Nobody will be able to touch you - once you belong to a cult, they will protect you," said Curtis Ogbebor, a community activist based in Benin City, who tries to stop young people joining groups like Black Axe. "The process of initiation - it's all about networking."

Dr Stone says many Axemen join solely for networking purposes. Nigeria has the second highest rate of unemployment in the world, and within this challenging environment, he says joining Black Axe can provide protection and business connections. He claims not all members are criminals.

"We have members in the Nigerian army, navy, air force. We have those in academia. We have priests, pastors," he said.

This mutual support was key to Black Axe's original purpose. The group grew out of a student fraternity called the Neo Black Movement of Africa (NBM). It formed at the University of Benin in the 1970s. The NBM's symbol was a black axe breaking chains, and its founders said their aim was to fight oppression. The NBM was inspired by the anti-apartheid struggle in South Africa, but in structure, secrecy and brotherly commitment, it mirrored societies like the Freemasons, which had a presence in Nigeria during the colonial era.

The NBM still exists today, and is a legally registered company with the Nigerian corporate affairs commission. It claims to have three million members around the world, and regularly publicises charitable activity - donations to orphanages, schools and the police, both in Nigeria and abroad. It holds huge annual conferences, some of which have been attended by prominent politicians and celebrities.

Leaders of the NBM claim Black Axe is a rogue, breakaway group. Publicly they strongly disassociate themselves from the name and are adamant that the NBM opposes all criminal activity.

"NBM is not Black Axe. NBM has nothing to do with criminality. NBM is an organisation that tends to promote greatness in the world," says Olorogun Ese Kakor, the current president of the organisation, in an interview with the BBC in July 2021.

The NBM's lawyers told us anyone from Black Axe who is found to be a member of NBM "will be expelled immediately" and that they have zero tolerance for crime.

International law enforcement have a different view. Statements by the US justice department, in the course of its prosecution of Black Axe members since 2018, say that the NBM is a "criminal organisation" and "part of the Black Axe". Similar statements have been made by authorities in Canada, who have said the NBM and Black Axe as "the same".

The documents seen by the BBC also appear to show links between some Black Axe members and the NBM corporation.

Many of the documents were sourced from an email account that belonged to Augustus Bemigho-Eyeoyibo, the president of the NBM between 2012 and 2016. These files suggest Mr Bemigho, a successful investor and hotelier in Nigeria, has engaged in large-scale internet fraud. The BBC verified two major cases from the data in which Mr Bemigho appears to have been involved in inheritance scams targeting UK and US citizens. The victims told us they were defrauded of more than $3.3m.

"We have removed him close to 1M dollar," says one message, referencing a victim, sent to Mr Bemigho by a suspected co-conspirator. The email contains the victim's full name, email address and number, and instructions on how to progress the scam.

The documents suggest Mr Bemigho sent scam formats to a network of collaborators on at least 50 occasions. One message, discussing the expansion of the NBM, suggests he requested members establish NGOs around the world in order to "rake in millions".

When messaging NBM members in the emails, Mr Bemigho addresses them as "Aye Axemen". In one response, which appears to have been sent to Mr Bemigho via Facebook messenger, he is addressed as "national elder Black Axe".

In 2019, Mr Bemigho's sister-in-law was charged with money laundering worth £1m in the UK. The Crown Prosecution Service, in a widely reported press release, referred to him as "the leader of the Black Axe" at the time.

When the BBC raised this evidence with the leadership of the NBM, they said they would investigate the matter, and that anyone found to be in breach of their code of conduct would be expelled. Mr Bemigho did not respond to the allegations when contacted by the BBC.

Dr Stone claims Black Axe and the NBM - beneath the surface - are the same organisation. He is speaking from experience. He was not only a member of Black Axe, but also a chairman within the NBM in their heartland of Benin City.

"It is one and the same," he says. "It's just a kind of formality to cover the informalities. It's a coin with two sides."

According to Tobias, the NBM has been instrumental in Black Axe's covert expansion around the world. "The Neo Black Movement as an organisation is just a charade, it's a smokescreen, it's a public face of the organisation," he says. He claims "the end game" of the NBM is "to subvert the opinion of the public"- to hide "what they really are, which is a mafia".

Organisations operating under the name of the NBM are registered around the world, including in the UK and Canada. There are at least 50 Facebook, Instagram and YouTube accounts using a variation of this name, in addition to the corporation's official social media channels. Some accounts have more than 100,000 followers. Others include implicit references to Black Axe - axe emojis, photos of people carrying axes or guns, and occasionally the signature slogan "Aye Axemen!"

The NBM has successfully established itself as a global brand, in multiple countries. In Nigeria, Dr Stone claims, the network's influence extends to the political sphere.

"There are a lot of members in the House of Assembly, even the executive," he said. "That is what Black Axe is. That is what NBM preaches: veer into any position that you know is humanly possible."

Augustus Bemigho, the former head of the NBM - described in UK court files as the former head of Black Axe - ran for office in the Nigerian House of Representatives in 2019, campaigning for the ruling All Progressive Congress Party (APC).

The activist Curtis Ogbebor claims Edo State politics is saturated with Black Axe members. "Nigeria has this mafia politics," he said. "Our politicians, government at all levels, encourage our youth into cultism."

Prospective Nigerian politicians, Mr Ogbebor claims, hire Black Axe members to intimidate rivals, guard ballot boxes, and coerce people to vote. Once in office, he says, they then reward them with positions in government.

"They arm them, they give them money during elections, and they promise them political appointment," he says.

Two documents, which appear to have been leaked from the internal communications of the NBM, suggest that 35m naira (more than £64,000) was funnelled to the organisation in Benin City to "protect votes" and ensure support for a governorship election in 2012. In exchange for the support, the files state "80 slots [were] allocated to NBM Benin Zone for immediate employment by the state government". This money was allegedly distributed directly "through the then Chief of Staff Hon. Sam Iredia" - who has now died.

During interviews with senior members of the NBM in Lagos, their legal representative confirmed that "a number of politicians" are members. He went on to name the Deputy Governor of Edo State, Philip Shaibu, as an example.

"There are a lot of people that are members of our organisation and there is nothing to hide about it," said Aliu Hope, one of the NBM's solicitors.

A former member of the Edo State government, speaking to the international media for the first time, has come forward to blow the whistle on Edo State's collaboration with organised crime.

Tony Kabaka, a self-confessed "cultist" and member of the NBM, spent years working for the government in Benin, up until 2019. During this time, through his company Akugbe Ventures, he employed more than 7,000 tax collectors, generating billions in revenue for the state.

Since leaving politics, Mr Kabaka has faced repeated assassination attempts. His mansion, a huge white building with Roman columns, is littered with bullet holes.

"If you sat me down and say, 'Can you identify Black Axe in government?' I will identify," he says. "Most politicians, almost everybody is involved."

Mr Kabaka claims he was asked to mobilise cult groups to help win elections. He denies ever being involved in violence himself.

"If government wants to seek for election they need them," he says. "Cultism still exists because government is involved, and that is the truth."

We travelled to Benin City in July 2021 to interview Deputy Governor Philip Shaibu, but he twice failed to turn up to the interview. When we sent the government of Edo State and Mr Shaibu our allegations that they have links to Black Axe, they did not respond.

Dr Stone believes Nigerian law enforcement and politicians are too enmeshed with Black Axe to effectively combat them. The solution to the violence, he says, lies within the cult itself. He is not the only former member who feels the group have become too dangerous.

"The reason some of us joined NBM was to join in the fight of oppression," wrote one member of a secret forum leaked to the BBC. "But now, we have been labelled a criminal organisation with evidence all over."

Internal Black Axe communications are littered with similar complaints from members.

"I didn't become an axeman to take lives, I became an axeman in the bid to fraternize," says another post. "Please, stop these killings."

The leaders of the NBM say they are committed to ensuring the organisation stays true to its founding principles and promotes peace. The group's current president, Olorogun Ese Kakor, told the BBC he was elected in order to root out criminal "infiltrators" and that these people are causing "the organisation so much harm". In a bid to harness this push for change, Dr Stone has formed what he calls a "Rainbow Coalition" - an advocacy group made up of former cultists, influential Nigerian citizens and professors. Members try to de-escalate tensions when rival gangs clash, and are trying to steer Black Axe towards a more peaceful future.

"Rainbow's contribution to society is to reduce criminality," he says. "To reduce the rate of death among youths. To reduce the rate of widows and orphans."

Rainbow's co-founder, Chukwuka Omessah, wants Black Axe members to reflect on the society they are creating.

"Everyone has a conscience," he says. "You may deny it on camera, deny it during public, but you cannot deny it in your quiet time - it will haunt you."

Dr Stone knows that pushing Black Axe towards reform is a dangerous business. He knows his former comrades might come for him one day. He is ready for them if they do. The professor keeps a three feet-long sword hidden in his car, and a licensed shot gun at home.

"For personal guard, personal safety," he says, with a half-smile. "If they come after me, can't I also come after them?"