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Eduardo Chaves used to spend most of the day asleep. Shortly after turning 16, he began working nights, delivering mangoes, bananas and acerola cherries to grocery stores in the rougher parts of Belém, a sweltering port city in the northern Brazilian state of Pará, near where the Amazon meets the Atlantic.

He needed the money. Unlike many of the other kids in Terra Firme, a violent neighbourhood of narrow alleyways, breeze block houses and low-slung power cables, he didn't drink, didn't smoke and wasn't that into clothing brands. But his girlfriend, Leonice Viana, had a baby from a previous relationship and he wanted to step up.

Most evenings, he went to college to learn how to run a small business, or else played video games with his younger brother. But on the night of 4 November 2014, Eduardo was with Leonice at his grandmother's house when the messages started to appear on Facebook.

António Figueiredo, 43, a corporal in Belém's Rondas Ostensivas Táticas Metropolitanas (ROTAM), the elite squad of the local military police, had been shot dead in the neighbouring area of Guamá. "Pet", as Figueiredo had been known since childhood, was well known in the area. Officially, he ran a private security business while he was off-duty. But in Guamá and Terra Firme, it was rumoured he worked for a death squad, killing suspected criminals for cash. At the time of his murder he was on medical leave after being shot in the knee. He was also being investigated over two homicides.

A few hours after his death, a message appeared on the official Facebook page of ROTAM: "Go with God, my brother! You fought the good fight and fulfilled your mission. Now let the hunting begin!!

You get that, scum... ROTAM's blood is up."

Pet's friends started posting messages calling for action. One, Rossicley Silva, another military police officer, wrote, "Friends, our little brother Pet (Corporal Figueiredo) has just been killed in Guamá. I am going. I hope to count on the maximum number of friends. We are going to respond. Sgt Rossicley."

'They killed one of our police officers and there is going to be a clean-up of the area. No one will protect you'

Then the WhatsApp messages began to appear: anonymous audio, sent from a friend of a friend. No one seemed to know the origin.

An authoritative male voice saying, "People, please, do whatever you need to, but don't go to Guamá, Canudos or Terra Firme tonight.

It's for your own safety. They killed one of our police officers and there is going to be a clean-up of the area. No one will protect you, not even the commissioner himself."

Leonice was frightened. She had left her baby with a neighbour a few blocks away. Now she wanted to pick her up in case there was trouble. Eduardo didn't want to let her go alone. His grandmother, María Auxiliadora, tried to persuade him not to leave.

María's house looks on to one of Terra Firme's central alleyways. As the couple turned the corner on to another street, a group of men on motorbikes appeared, their faces hidden by helmets.

In her account to a local TV station, before she fled the city, Leonice described how one of the men ordered them to stop. A black car blocked the alley behind. Leonice was told to let go of Eduardo's hand. She tried to grab him, but they pushed her away.

The men started beating him, shoving his head against the wall.

Eduardo raised his arm, screaming that he was not a criminal. The first bullet went through his hand, then four more were fired into his head. His father found his body in the street.

A further nine people were killed that night in Belém. In six of the murders, including Eduardo's, the casings found at the scenes came from .40 calibre pistols, the standard issue firearm for military police in Pará. "What they did to him, you wouldn't even do to an animal," his grandmother told me.

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Death squads comprising off-duty police officers and other members of the state security forces have long been a feature of the criminal ecosystems of Rio de Janeiro and São Paulo.

There is increasing evidence that such groups operate elsewhere in Brazil - and it's only getting worse.

In October 2014, an escaped prisoner in the northeastern city of Poço Verde was shot dead by police, reportedly during a shoot-out.

But the dead man's widow told a TV interviewer that her husband had been sitting on the sofa with his four-year-old daughter when the police broke into their home. Although the man offered to surrender, they shot him in the head.

By Brazilian standards, it was an unexceptional death, but for the fact his killing was linked to a death squad that had been under investigation for the previous six months. Seven police officers and military personnel were subsequently arrested. It was the fourth operation against death squads in Brazil's northeast in the past three years; at least 45 serving police officers have been arrested.

In Pará, there have been five massacres over the past five years; in all five, police officers have been accused of involvement. In one incident, in November 2011, a group of six teenagers were shot dead in the street by two men on a motorbike. A former police officer was convicted in October 2014 and sentenced to 120 years in prison. The second suspect has never been found.

These were the headlines on the front page of the Diário Do Pará the day I arrived two weeks after the attacks: "12 Paraenses Killed Every Day"; "Man Steals R$100,000"; "Boy Is Killed With 36 Stab Wounds"; and "Police Officer Is Shot After Responding To Assault". The top story was the work of JR Avelar, the only journalist in the state with a police radio, a gift from a parting police chief grateful for his positive coverage. Over the three decades he has spent working the crime beat, Avelar has cultivated an extensive network of police officers, hospital workers and morgue attendants.

His smartphones constantly buzz with photos of corpses sent via WhatsApp. In our first meeting, Avelar briskly swiped through a few snaps of the bloodied, bullet-ridden bodies of three plain-clothes police officers, a picture of a beautiful woman whose back had been ripped apart by shark's teeth, and the image of a suspected rapist whose anus had been plugged with a thick wooden stake.

But most of the dead are young, black or mixed-race men shot to death in one of the poorer bairrosof Belém. If the victim is worth a story, Avelar will ensure the photo is published in the Diário Do Pará. A few years back, a hard-fought judicial ruling granted the paper the right to print images of the dead, but only with faces pixilated - a restriction Avelar regards as a contemptible attack on press freedom.

A short, wiry man with a smartly clipped salt-and-pepper beard and aviator sunglasses, Avelar dresses all in black, with combat trousers and a long-sleeve shirt with his name sown in yellow stitching above the left breast pocket. Though crime is his staple, the biggest scoop he ever had was a photo of a baby with two heads. "That sold round the world," he said.

It was an airless Friday night in late November and we were parked underneath one of the mango trees that line the city streets outside the homicide division of the civil police.

I shared the back seat of Avelar's car with a bulletproof vest and several thick rolls of police tape. "I buy my own," he told me. "I seal off the crime scene myself when I get there. Each roll costs around R$40 (£10) but the police don't want to spend that money, so they are always happy when I turn up at a crime scene with mine."

I asked him about the recent killings. "The police say they are investigating," he said. "If you want my opinion, they won't get anywhere. It's not in their interests."

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Murder is one of Brazil's most distinctive industries. More than 53,000 Brazilians were killed in 2013: one every ten minutes. More people have been killed in Brazil over the past four years than in Syria's civil war. The overwhelming majority of Brazil's victims are young, male, black and poor.

Brazil's police force is divided into three: military, civil and federal. The military police patrol the streets, and despite the dangerous nature of the job are paid less than their civil counterparts. Co-operation between the civil and the military forces is often strained, undermining the police's capacity to solve crimes.

The police make their own substantial contribution to the murder rate. According to the Fórum Brasileiro De Segurança Pública, a security think-tank, Brazilian police killed an average of six people every day in 2013. Between 2009-2013 the police killed 11,197 - more than the total number of people killed by police in the US over the past 30 years.

That number is likely to be an underestimate. Samira Bueno, the think-tank's director, believes police in Brazil are not in the habit of recording police lethality. "There is an under-reporting," she said. Each year, a further 15,000 deaths are categorised as "to be clarified".

But the police, particularly the military branch, are also the victims of Brazil's violence. Over the same five-year period, 1,170 police officers were killed. They are much more vulnerable off-duty, when they are almost three times more likely to be killed.

Police officers can be targeted because of their weapons. For Brazilians outside of the security forces it is extremely difficult to purchase a gun legally. The police, however, are licensed to carry weapons even when off-duty. "Corporal J", a military police officer in São Paulo who spoke on condition of anonymity, told me that when he started in the police 21 years ago, the biggest risk to life came during working hours. "Now, the risk is constant," he said. "If some criminal finds out you are moonlighting in a certain area [common practice among Brazil's low-paid police officers] he will try to rob you for your gun or even kill you for it. A policeman on his own is running a big risk."

The low conviction rate of Brazilian homicides, estimated at between five and eight per cent by the nonprofit Brazilian Criminology Association, means that killing a police officer or a security guard is often the most rational option in the commission of a crime.

For the police, it also makes sense to shoot first. If a suspect is killed by a police officer, the homicide is almost always classified as auto de resistência [literally, "act of resistance"], which effectively shifts the blame for the death on to the victim himself and removes the need for an internal investigation.

Bruce Christian, a 14-year-old boy riding on the back of his father's motorbike in the northeastern city of Fortaleza, was shot dead by police after his father failed to heed a command to stop.

Ricardo Prudente, a 39-year-old advertising executive, was killed after police mistook his mobile phone for a gun. Local news reported Flávio Ferreira Santana, an unarmed dentist, was shot dead by police who then altered the crime scene and left a gun in his hand. All were classified as autos de resistência.

'If a police officer feels threatened or he thinks his family is at risk, he will carry out justice with his own hands.

That's natural'

I asked Corporal J if the police sought out criminals to kill when they were off duty. "Sometimes," he said. "If a police officer feels threatened or he thinks his family is at risk, he will carry out justice with his own hands. That's natural." Such a killing, he told me, would be investigated like any other murder. "If they find a suspect, they will charge them. If not, they leave it and... forget about it."

Brazilians have a low level of trust in their police, but an even lower level of trust in their criminal justice system. Brazil has the world's fourth-largest prison population, with more than half a million people incarcerated, but just over 40 per cent awaiting trial. Still, many Brazilians think the state is far too lax.

Roberval Conte Lopes, a São Paulo city councillor and former commander of an elite military police squad, gave me the example of Zé Galinha. "He was a criminal who surrendered after a shoot-out with police. He was released after a month and then went on to rape and murder a young girl," he said. "I think it would have been better if he'd been shot. Don't you?"

Conte Lopes received a degree of national fame following the publication of ROTA 66 - The History Of Police Who Kill, a prize-winning book by Caco Barcellos, which claimed Conte Lopes had participated in a death squad that killed hundreds in the city in the Eighties. In his own book, To Kill Or To Die, Conte Lopes denies being part of a death squad but freely admits to killing at least 42 people. "And I don't regret a single one," he told me.

Though repeatedly investigated, he has never been charged with any crime and has been elected to public office many times. There is a widespread acceptance in Brazilian society that most killings by police are probably justified. Bandido bom é bandido morto. A good criminal is a dead criminal.

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In Belém, I visited Terra Firme a few weeks after Eduardo's death. Human-rights groups, along with a few state legislators, the residents of the bairro and the families of those killed, were holding a protest to demand an investigation into the murders.

Around a hundred demonstrators ambled through the dusty streets one Sunday morning, under a relentless equatorial sun, accompanied by an incongruously upbeat band and a grey Ford Escort, struggling over the neighbourhood's vicious speed bumps with the weight of its massive sound system. The march followed the route the death squad had taken through the area. At the place where Eduardo was killed, María Auxiliadora held up a poster on which she had stuck a photograph of her grandson and a handwritten message. "I am a sheep and I can be found by the side of my shepherd: the Lord Jesus." "He went to church," she said, uncomprehendingly. "It was just that he was weak. It's not right that they should do that, just because he had strayed a little." She started sobbing and was unable to continue.

It was unclear what she meant. Eduardo's grandfather, Raimundo Alonso, and his father, Sergio Chaves, told me that Eduardo had never had any problems with the police and had no involvement with drug trafficking.

But another prominent local journalist, Amaury Silveira, the father of two military police officers, had told me earlier that all the victims of the night's killing had been selected in advance. "None of the guys they killed were innocent, except for one of them, who was just a bus fare collector." Still, not a single one of those killed had a police record.

Rosenil Alves, a 46-year-old woman who has lived in Terra Firme since she was a teenager, was standing in front of her house, watching the demonstration go by. She told me how she spent the night that Pet, Eduardo and the others were killed standing by her window, watching the police cars, the ambulances and finally the reporters. "I received lots of messages on WhatsApp that night.

That's what terrified me. My God, I thought to myself, can they really have killed that many people?"

All across Belém that night, messages were posted on Facebook and WhatsApp claiming that dozens of people all over the city were being killed. Horrific images, many culled from internet reports of unrelated incidents, were passed between friends as evidence of an ongoing bloodbath. "There was total panic," Samuelson Higaki, the investigating officer from the civil police's technological crime unit, told me. "The next day people stayed at home. No one wanted to go into the street. People were claiming there were shoot-outs, that the police were picking people up at random."

On 5 November, Luiz Fernandes Rocha, then security secretary for the state of Pará, gave a press conference in which he said ten people, excluding Corporal Pet, had been killed overnight. A contact at Belém's city morgue said the real figure was closer to 80, and that the mayhem that night had provided cover for the elimination of undesirables. The civil police told me that number was "unfounded".

Six of those killed, including Eduardo, were executed by masked men riding motorbikes. "We believe these murders were carried out by the same group," Fernandes Rocha said. "We are also investigating whether these crimes were committed by police officers."

As for the messages that appeared to have been posted by the police, Higaki would only tell me that some police officers were among the suspects, but no arrests have been made. Rossicley Silva told theWashington Post his Facebook post had been misinterpreted. He has been temporarily moved from frontline police work to an administrative post.

Ten days after the massacre, Layane Gomes Soares, a girlfriend of Pet, was shot dead by two men in a suburb of Belém, apparently on the orders of a jealous imprisoned ex-boyfriend.

That same day, the police arrested Henrique Cardoso Souza, also known as "Bigfoot", an alleged member of Equipe Rex, the gang which controls the drug trade in Terra Firme, on suspicion of Pet's murder. Half an hour after he was released he was gunned down by someone firing from the window of a black car. "There is a death penalty for people who kill police officers,"

Dr Isabela Oliveira das Neves, a former cop turned human rights investigator told me. "It may not be legal, but it's a fact."

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Avelar took me to meet another friend of Pet, who agreed to speak to me anonymously. "Sergeant S" is a serving military police officer, in the force for more than 20 years. Until recently he managed to combine a career in ROTAM, the same elite squad that Pet belonged to, with a vocation as an evangelical pastor.

A large, powerfully built man with a shaved head and a gold chain around his neck, S welcomed me warmly into his home, accessed via the metal door of a garage, in a quiet residential street.

Despite repeated threats to his life, S told me the house had no special security system in place other than some internal cameras and "the protection of God".

S seemed vaguely amused throughout most of the interview. But when irritated by a line of questioning his eyes narrowed. "He's pretty tough," Avelar had told me. "He really goes after the bad guys."

Born and raised in Belém, S lives with his wife of 23 years, three children and his mother in the neighbourhood where he grew up, though he told me that for his own safety he does not spend much time on the streets any more. A few months ago, he was leaving the gym when he was attacked by three armed men in the car park of a supermarket. He managed to shoot one of them and the other two fled. S said that he was lucky to have never been injured in his career, although he did bear "wounds of the soul". Most weeks, he told me, he was involved in a shoot-out at work.

Two major events had changed the way he thought about policing.

One was the killing of a close colleague; the other was when a stranger begged him for help after receiving a death threat. "I told the guy to leave me alone. That very day they killed him. So now if anyone comes to me asking for help - big or small - I will do it because that way I can stop bigger problems."

'If someone is killed, it's not me who is doing the killing. It's the state. The state gives me this power'

Sergeant S said that he had only ever killed people in self defence. "I have never regretted killing anyone. I sleep well at night. I have been investigated over four cases and I have never been prosecuted. There are still three lawsuits outstanding against me, but I have never regretted anything I have done. I always did my duty. I don't have any problem shooting someone who is threatening me or any another law-abiding person. My job is to protect people. And if someone is killed, it's not me who is doing the killing. It's the state. The state gives me this power."

I asked him how many people he has killed. "I have no idea. I can't remember. That's something we don't talk about."

As for the murders on the night of 4 November, S claimed the victims were criminals fighting over territory. "The police had nothing to do with those deaths."

In the wake of the murders, the parliamentary assembly in Pará launched an investigation to determine whether death squads and militias were operating in the state. I asked S what he thought of the inquiry. "Ridiculous," he shouted, momentarily losing his cool. "They're crazy. They're attacking the most vulnerable part of the state: the police."

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On 30 January 2015, the Pará state assembly released its 226-page report. It concluded that there were at least four militias operating across the state, all of them with some level of participation from the military police, funded by drug trafficking, racketeering and contract killing. Wiretap evidence presented to the inquiry revealed that militia members charged between R$200 (£50) and R$15,000 (£3,500) per kill.

At least 60 people, among them serving police officers and politicians, were accused of involvement in militias. The report's authors concluded that Corporal Pet was murdered by members of his own militia in a dispute over money and called for Sergeant Rossicley Silva, the man who appeared to co-ordinate the massacre of 4 November, to be indicted.

No one has yet been arrested in connection with the killings that night, though the state police force insist the investigation is ongoing. Few of those involved in compiling the report expect the police to find sufficient evidence to prosecute individuals.

The police have made one arrest since the assembly concluded its inquiry. Otacílio José Queiroz Gonçalves, a former military police officer known as "Cilinho", was arrested on 9 February on an outstanding homicide arrest warrant that predates the November massacre. Retired from the police ten years ago after being diagnosed with schizophrenia, Cilinho ran the Guamá militia along with Pet, according to the report. In the meantime, the violence continues in Belém. In late February and early March, there were serious riots in five of the city's overcrowded jails. Nine municipal buses were also set on fire by gangs linked to the inmates. "Organised crime is moving into Belém," Avelar wrote to me via WhatsApp. "They're copying Rio."

For the security forces, there are other, more pressing, priorities. Avelar believes the arrest of Cilinho will be the end of the state's efforts to investigate militias or find those responsible for the killings of 4 November. "They found a scapegoat," he wrote. "Now they'll just forget about it."

Originally published in the July 2015 issue of

British GQ