At 5.13pm on Thursday 12 May 2016, a young man named Abdul Wahab Hafidah was seen on CCTV cameras running westward through busy traffic across Princess Road in Moss Side, a crowded, diverse, working-class neighbourhood two miles south of Manchester city centre. He was pursued by two young men on foot, and another on a bicycle. As traffic slowed at the junction of Princess Road and Moss Lane East, Hafidah tried desperately to open the door of a passing car, before turning to face his pursuers, waving a knife. They stepped back, and he ran off down Moss Lane East. Someone threw a hammer at him, but missed. The chase went on, joined – or followed – by seven other young men who made their way across Princess Road over the next 45 seconds.

Hafidah was drunk, and he was scared. He knew some of the boys who were chasing him, and he knew they were angry with him. On Moss Lane East, he tried once more to get into a passing vehicle. As he ran across the street, he was hit by more than one car, one of which was a Vauxhall Corsa, driven by a friend of some of those pursuing him. A pathologist later found that he had suffered leg injuries suggesting “a glancing blow” at low speed.

At around 5.14pm, near the junction of Moss Lane East and Denhill Road, roughly 100 metres west of Princess Road, several of Hafidah’s pursuers caught up to him. He was punched, kicked and stamped on, although witnesses remember the details and the number of attackers differently. According to statements taken by the police, a student walking home from college saw “at least three or four” people drag Hafidah to the ground, punching and kicking him. A man working in an office overlooking the scene saw “a couple of youths” fighting on the northern side of the road, and “six or seven youths” watching from a nearby grass verge. Another witness, a lab assistant, thought there were five attackers. A woman on her way home from work saw three young men knock Hafidah to the ground. He curled up into a ball while they kicked him around the legs, torso and head.

“Don’t you think you’ve done enough? Get off him!” the woman coming home from work shouted at the assailants, according to her witness statement. All but two ran away; one of those two continued to beat Hafidah. The lab assistant thought the other young man was telling the attacker to leave it and run, but that the attacker ignored him. The attacker was “really angry”, she thought, and was shouting at Hafidah as he kicked him. She noticed that the attacker’s face was covered, and that he was wearing gloves, despite the weather that day, which was clear and warm.

Then he bent over Hafidah and stabbed him in the neck. The attacker ran off after the others, most of whom were already at least 20 metres away. The assault had lasted 30-40 seconds.

“No, no, no,” the lab assistant cried as she ran towards Hafidah. “Not another one of our boys!” A man on his way home from Asda tried to press the victim’s hood against his neck to stop the bleeding. With some of his last words, Hafidah asked this man to tell his family that he loved them. Paramedics arrived. The shopper and the lab assistant sat on the grass verge and cried.

Hafidah died two days later in Manchester Royal Infirmary. He was 18 years old.

In the weeks following his death, 17 young people were arrested in connection with the killing. The young man who stabbed Hafidah – who would eventually admit to the crime after he was sentenced to life imprisonment in September last year – was a 19-year-old named Devonte Cantrill. A six-month investigation led police to the same conclusion. In an interview room at Longsight police station on 15 November 2016, Cantrill was asked several times why he committed the crime.

“We explained to your solicitor that our enquiries so far would suggest that you were the person that put a knife in Abdul Hafidah’s throat,” a detective constable told Cantrill. “I’m suggesting to you that you are the person that has killed Hafidah. Let’s be as direct as that.”

But shortly after that interview, Cantrill and 12 other young people were charged with the murder. Most had no criminal history. Before the fight that led to Abdul’s death, most of the group had spent the afternoon hanging around a local park, listening to music or kicking a football around. One had spent it with his infant son, and two of the other accused were about to have a baby together. Prosecutors alleged they were members of a gang and had intended, as a group, to assist in the killing. Last summer, four of them were convicted of manslaughter, including Devon’ta Neish, 17, who was on a bicycle at the back of the group chasing Hafidah, and never got off his bike to attack him. Their sentences range from five to 12 years.

Cantrill and six others were found guilty of murder. These included Nathaniel Jermaine Williams, 17, the driver of the Corsa, a keen footballer who worked part-time in Nando’s – who did not get out of his car during the fight – and his school friend Reano Walters, 18, who seemed from mobile phone footage shot in the aftermath of the attack to have been around 20 metres away at the moment of the stabbing. Williams and Walters had spent part of the afternoon driving around in the Corsa, just passing time and showing off to girls in the neighbourhood, Walters later testified. The prosecution had accused them of conducting a “high-visibility patrol” of their alleged gang territory. All seven young men found guilty of murder were handed life sentences, with a minimum tariff of 23 years for Cantrill, and sentences ranging from 16 to 20 years for the six who had not stabbed Hafidah.

How did a stabbing by one young man lead to 11 convictions? The answer is one of the most controversial principles in English law.

There are a number of ways a person can be convicted for a crime in which they did not play the decisive role – or even, perhaps, any role at all. Collectively, they are known as “joint enterprise”, a principle of common law stretching back hundreds of years. In one well-known case, from 1952, Derek Bentley was convicted of murder after his accomplice in a burglary, Christopher Craig, shot a police officer. “Let him have it, Chris,” Bentley had said, perhaps telling Craig to hand over his weapon – or perhaps, as the prosecution argued, urging him to fire. Under joint enterprise, Bentley had provided what is known as “assistance or encouragement” and was therefore just as guilty as Craig, the “principal” offender. Bentley received a pardon in 1998, although he had been executed by hanging 45 years previously.

‘Let him have it’ … Derek Bentley, who was hanged for a shooting in which he was not holding the gun. Photograph: PA

A more recent controversial example was the conviction of Laura Mitchell and her boyfriend, Michael Hall. One night in 2007, the couple, and two other people they were with, got into a fight in a car park outside a Bradford pub, with a man named Andrew Ayres, over who had booked a taxi. Mitchell and Hall then left the scene so that she could search a different part of the car park for her lost shoes. In the meantime, the other two defendants went to a nearby house and armed themselves with knuckledusters and other weapons. In a second, more serious fight, which did not involve Mitchell or Hall, Ayres was killed. The two armed men were convicted of murder, but so too were Mitchell and Hall. Their convictions were upheld by an appeals court in October 2016.

In another case often cited by campaigners against the abuse of joint enterprise, Jordan Cunliffe, who was then 15, was one of three people convicted of the 2007 murder of Garry Newlove. Newlove was killed by a kick to the neck by one of a group of local teenagers, who attacked him after he accused them of vandalising his car. Cunliffe argues that although he was present, he never touched Newlove – a claim supported by the fact that he suffers from a degenerative eye condition, and was registered as blind at the time. “If you can do that to a blind 15-year-old, you can do it to anyone – and obviously it’s been done to a lot of people,” his mother, Janet, said to the Guardian two years ago. Cunliffe remains in prison.

There could be more than 1,000 similar cases. The government does not collect statistics on joint enterprise; officially, a joint-enterprise murder is just another murder, and it is difficult to be sure whether or not prosecutions are becoming more common. But one study, by The Bureau of Investigative Journalism (TBIJ), found that between 2005 and 2013, 1,853 people were prosecuted for homicides involving four or more defendants. Such cases consistently represented about 15-20% of homicide prosecutions each year.

Joint enterprise has also come under increasing scrutiny in recent years because of a growing body of academic research that appears to show it is applied disproportionately against black defendants. According to one study, black people are serving time under joint enterprise at 11 times their presence in the population as a whole. All of these issues have been at the forefront of a campaign to reform joint enterprise law, led by Jengba (Joint Enterprise Not Guilty By Association), a group representing the family members of nearly 1,000 people locked up under joint enterprise.

It’s not that joint enterprise is always wrong in principle. “An example I always give in which joint enterprise is not remotely problematic would be where four people attack the victim, three of them hold him down, and the fourth one stabs him,” said Simon Natas, a partner at ITN Solicitors in London, who has acted for Jengba. “They’re all guilty of murder. It doesn’t matter that the other three are not wielding the knife.”

But the trouble is that homicides are not always so straightforward, especially in cases of spontaneous violence, such as a street fight. One defendant might throw a few punches without intending that anybody should use a knife. Should their commission of assault imply their guilt of murder? And what about defendants like Cunliffe, who were present at a killing, but did not participate, or Mitchell and Hall, who weren’t present at all? In their 2014 study, TBIJ found countless examples of people incarcerated for murder or manslaughter in situations like these.

The increasing visibility of such convictions in the last decade-and-a-half has caused joint enterprise to suffer from what the Prison Reform Trust calls a “deficit in legitimacy”. Thirty-seven of 43 lawyers interviewed by TBIJ expressed concern about the way the law operates.

Joint enterprise’s crisis of legitimacy has also been intensified by its grossly unequal application. In a study of the cases of 294 people under 26 who were given sentences of 15 years or more, researchers at Cambridge University found that those convicted under joint enterprise comprised more than half of their sample, and observed a stark pattern in the composition of this group: more than half were black or mixed-race.

Black and mixed-race people are already over-represented in the criminal justice system, as a report by David Lammy MP, in 2017, documented in painful detail. But even taking their disproportionate presence in the system as a baseline, black and mixed-race prisoners convicted under joint enterprise were over-represented by a factor of three in the Cambridge study.

The vast majority of homicides in England and Wales – like the vast majority of most crimes – are committed by white people, who make up 86% of the population. But the patterns found in the Cambridge study have been frequently reproduced by other researchers. It seems there is something different about joint enterprise. A Prison Reform Trust study of 61 joint-enterprise cases involving 157 defendants found that for defendants whose ethnicity was known, around two-thirds were from ethnic minorities. More than 40% were black. Almost two-thirds were under 25. Similar disproportionality has been found by researchers at Manchester Metropolitan University. Ethnic-minority joint-enterprise prisoners are younger than their white counterparts when convicted, are tried with a larger number of co-defendants and serve longer sentences.

All 11 of those convicted in the Moss Side case are black or mixed-race. The youngest was 14 at the time of the attack, and the oldest was 20. Their family members say that the academic research confirms their fear that their loved ones have been convicted in part because of the colour of their skin. “The jury made up their mind as soon as they saw them,” said Devon’ta Neish’s aunt Anna, an administrator at a local school. “They saw black boys from Moss Side, they heard ‘gangs’, and that was it.”

A joint enterprise case, perhaps more than most murders, requires a narrative. The jury must be made to understand how a fractured and sometimes confusing evidential picture, involving multiple participants with different types and levels of involvement, should be assembled.

After years of growing controversy, a landmark supreme court decision in February 2016 appeared to set a stringent new standard for joint enterprise convictions. In “R v Jogee”, the court ruled that mere foresight that a crime such as murder might occur was not sufficient grounds for convicting a secondary offender. Instead, the prosecution would have to show that a defendant also intended for the crime to be committed. Campaigners and legal scholars hoped this would put an end to disproportionate joint enterprise convictions, but the successful prosecution of the Moss Side case has cast this into doubt.

In terms of the number of defendants, the Moss Side case was one of the largest ever joint enterprise murder trials. According to the prosecution, there was only one way to assemble the pieces of the story: the defendants were part of a criminal gang, determined to attack en masse a member of a rival gang. As the judge explained in his directions to the jury: “When two or more persons join together to chase and to attack someone, each is liable for the acts done in furtherance of their joint purpose.”

Abdul Wahab Hafidah, who was murdered in Manchester in 2016. Photograph: Greater Manchester Police

In order to be found guilty under joint enterprise, a defendant must meet two criteria: the first relates to their actions, and the second to their state of mind. In the Moss Side case, the prosecution argued that each defendant had acted in some way to contribute to the fatal attack – by beating up Hafidah before he was stabbed, by helping to chase him down or by offering implicit support through their presence. In law, this is known as the “conduct element”: an action that facilitated the offence of the principal offender.

Prosecutors must also demonstrate a “mental element”, relating to the state of mind of the “secondary” defendant – the one who did not directly commit the crime. According to the new standard set by the Jogee decision, to be found guilty, a secondary defendant must share the same intention as the principal defendant. In the Moss Side case, this meant demonstrating their intention to kill or, in the words of the judge in the Moss Side case, “at least cause some really serious injury”.

But R v Jogee did not do away altogether with the question of “foresight” that a crime would be committed: while it was no longer enough to convict a secondary defendant just by showing that they could have foreseen a murder, the fact of that foresight could still be used as evidence of shared intent. The prosecution in the Moss Side case pointed to the presence of a hammer during the chase, and the possibility that a defendant other than Cantrill might have also had a knife, to suggest that the defendants must have foreseen that weapons would be used, fatally.

If the Moss Side defendants could foresee the use of a deadly weapon and still continued the chase, the prosecution argued, they must have intended it. This seems to make the Jogee decision much more equivocal than many activists had first hoped. “If intention can be readily inferred from foresight, then nothing will have changed,” Beatrice Krebs, an associate professor in law at the University of Reading, said. “But it depends, of course, on what is happening in practice.”

The Jengba lawyer Simon Natas disagrees that knowledge of weapons always demonstrates a defendant’s intention that serious harm should be caused. “You need to look at what that knowledge actually implied, what their conduct was in relation to the weapon, what their conduct was in the course of the incident,” Natas said. Hafidah was not struck with the hammer, nor was he stabbed by anyone other than Cantrill. If the others were carrying lethal weapons and intended to use them against Hafidah, why did they not do so?

Some of the defendants say they only ran after the commotion to see what happened, or, like the 29-year-old Cordell Austin – the only defendant to be acquitted – to look out for the safety of younger boys. Those who appeared, in CCTV footage, to be near the front of the chase as it crossed Princess Road said they had disengaged before the fight began. (The fight itself was not caught on camera.) Nobody admitted to having participated in the attack itself, perhaps afraid of incriminating themselves, or of being forced to describe the actions of others.

Some of the defendants knew Hafidah, and regarded him with a mixture of fear and hostility. Local youth workers knew him, and had had concerns about him – he was someone they wanted to protect, but they also knew he had been responsible for violence against others. Some of the boys had been attacked or threatened by him in the past, or knew of others who had been. Some, though not all, likely bore a grudge against him.

In the five or so minutes before the chase began, the group were hanging around in a park by Westwood Street, chatting and listening to music. Hafidah was hiding in the grounds of a nearby derelict building. According to the courtroom testimony of several defendants, Hafidah began throwing stones at one of their cars. His judgment impaired by alcohol – he was around 1.5 times over the drink-driving limit – he might have been trying to engineer a confrontation.

In this reading, the chase that ensued was spontaneous, with each participant having a different understanding of what was going on, and what would happen if Hafidah was caught. “Probably two or three of them actually wanted to have a fight with him,” according to Akemia Minott, a local youth worker who knew most of the defendants. “Others wanted to see what was happening. I think one had the intention to stab him.”

But the claim that the defendants were members of a gang helped prosecutors argue that they shared the same joint purpose, no matter how peripheral their conduct was to the act of killing Hafidah. According to the crown’s QC, Nicholas Johnson, the chase was “a co-ordinated effort” involving all 13 defendants.

Even the most trivial facts became evidence of this gang intention, including some that might have also suggested a lack of coordination. Devon’ta Neish, for example, took a slightly different route as he followed the others towards Princess Road. The prosecution argued that he was trying to “head off” Hafidah in the hypothetical event that he attempted to double back and escape. Rather than a spontaneous fight taken to another level by one angry young man, in the prosecution story, each defendant had played his role in the gang violence.

Hafidah sustained dozens of injuries from the many blows he received on Moss Lane East, but the pathologist judged that none of these contributed to his death. After a woman shouted at the attackers to stop, only Devonte Cantrill continued to attack Hafidah. He had been the last to arrive at the scene on Moss Lane East. He was the only attacker to cover his face, to wear gloves, and to strike Hafidah with a weapon. According to one witness, he seemed to be in a state of fury.

Cantrill had had some difficult times in his life, and it was not the first time he had been violent. By the time he was arrested for Hafidah’s murder, he had been kicked out of the bail hostel where he was living in Salford, and was homeless. He had a previous conviction for head-butting a PCSO, for which he received a custodial sentence. While inside, he attacked a prison officer. “I was an angry kid back then,” he told police when asked about these incidents. He also told them that once, when he was in Deerbolt young offender institution, he went to the doctor for help with his mental health. But, he said: “I didn’t even chat to her properly. I spoke to her and then two days, three days, I got shipped out.”

The rhetorical association of minority – especially black – youth, with gangs and violence is a persistent feature of the British criminal justice system. And alleged gang rivalry is a frequent element in joint enterprise prosecutions. Becky Clarke and Patrick Williams, researchers from Manchester Metropolitan University, found that almost two-thirds of joint enterprise prisoners reported that “gang” links had been alleged during their trials.

There is not only a racial disparity in the application of joint enterprise; there is also a racial disparity in the use of “gang” evidence in prosecutions. Clarke and Williams found that 78.9% of ethnic-minority joint enterprise prisoners had been described as gang members by prosecutors, compared to only 38.5% of whites.

Although young black people are more likely to be suspected by the police of being gang members, they commit a proportionally small amount of violence. In their study, published in 2016, Clarke and Williams found that 81% of the individuals on Greater Manchester police’s list of suspected gang members were black. Yet during the same period, black youth were responsible for just 6% of serious violence by young people in Manchester. Similar patterns were found in London, where Metropolitan police data showed that in 2015-2016 less than 5% of serious youth violence was linked to alleged gang members. “Serious youth violence does not equal gang crime,” the former deputy mayor for policing and crime, Stephen Greenhalgh, has said.

Members of Jengba demonstrate outside the Royal Courts of Justice in London. Photograph: PA

To Clarke, the disparity between the policing priorities and the reality of offending is striking. “When you plot the youth violence data on a map, you see these hotspots in north Manchester and Wythenshawe, and little ones in central-south. About 70% of the people who represent all of the marks on those hotspots were white British.” But when you look at the map of alleged gang members, “there’s just this one big hotspot, right in Moss Side.”

The evidence of gang membership that prosecutors bring to bear in joint enterprise trials is often of questionable merit, according to Clarke and Williams. In the Moss Side case, the prosecution alleged that a few of the defendants were linked to the gang “Active Only” with photographs from the defendants’ social media accounts in which they made what the prosecution claimed were gang “hand signs”. According to DCI Terry Crompton, who led the murder investigation in this case, this evidence represented “self-admission” of gang membership.

The boys and their families reject this. “Get any boy from round here, they don’t like to just stand straight in a picture, they love to do something with their hands,” a sister of one of the defendants said. “You’re calling these boys gang members for doing what you’re paying rappers to do on the TV.”

The 13 defendants were not a particularly close group, but it was easy to find links between them. Moss Side has been the heart of Manchester’s African-Caribbean and African communities since the 1950s, and it was easy for police to identify social or family connections between the defendants, which were then characterised as gang associations.

“We know you’re best buds with Durrell Ford because all your profile pictures are the same on Facebook,” an officer trying to portray the boys as gang members said to Durrell Goodall, 19, an amateur athlete who was among the second group to chase Abdul across Princess Road. Ford was also 19, and the two boys had been friends since Goodall’s mother moved to Moss Side when he was seven, having found the east Manchester neighbourhood of Clayton too racist to raise a mixed-race boy. Two of the other boys played football together, others went to the same youth club, or were neighbours.

For Crompton, these links were enough to suspect all the defendants of being gang members. “We have some clear evidence from self-admissions,” he told me, referring to the photographs in which some of the young men made hand signs. Some of the others “may or may not be” gang members, he added, “but they certainly associated together, at least on the day”. In court, the prosecution tried to finesse these ambiguities by suggesting that any defendants that were not actually gang members were “affiliated with or sympathetic to” the gang, but Crompton admitted that these were not terms he could define.

Surprisingly, given the focus on the Active Only gang during the trial, a “senior police source” initially told the Manchester Evening News, 12 days after the murder, that it had been committed by a gang called the Moss Side Bloods. Months later, during police interviews in November 2016, several defendants were still being asked about alleged associations with that gang.

But when I asked Crompton about how soon investigators had determined that Active Only was responsible, he said it had been “pretty quickly” after the killing. (When I reminded him of the Moss Side Bloods theory, he said he wasn’t sure that gang still existed.) It was hard to avoid the conclusion that the gang theory might have been formulated before police knew which gang to attribute the violence to. Similarly, Crompton doubted that you could map the territory allegedly controlled by Active Only – a direct contradiction of what a police expert witness said at the trial.

There is a striking discrepancy between the more complex picture admitted privately by the senior police officer who led the investigation, and the certainty with which the prosecution presented the case in court. While youth violence is a very real problem, the “gang” framework is shaped primarily by police wishing to impose order on a situation that is fundamentally chaotic. This imposed order creates the narrative clarity that enables joint enterprise convictions.

For the family members, this practice represents bad faith. “Some of the things they’re saying – you know they’re blatantly lying about your children,” said the mother of Reano Walters, who was convicted of murder and sentenced to life with a minimum term of 20 years. “You know they’re lying. Deep down in their hearts, they know that half of what they’re saying is a lie.”

In responding to the challenges of youth violence, some seem more interested in getting convictions than securing justice. “What you’ve got to decide is not: ‘Does the system lead to people being wrongly convicted?’,” the former Labour lord chancellor Charles Falconer told the BBC in 2010, while discussing joint enterprise. “I think the real question is: ‘Do you want a law as draconian as our law is, which says juries can convict even if you are quite a peripheral member of the gang which killed?’ And I think broadly the view of reasonable people is that you probably do need a quite draconian law in that respect.”

But concerns about the dual injustice of joint enterprise – both in overcharging individuals for their roles in crimes, and in the racially disproportionate way the law is applied – have dogged joint enterprise for years, as reports by the House of Commons justice select committee noted in 2012 and 2014. Lucy Powell, MP for Manchester Central, believes that these fears have been proven right once again in the case of Hafidah’s murder.

“Charging 13 people with murder, when clearly 13 people were not actually involved in the act of murder directly, I thought was disproportionate,” Powell told me. “And I think a lot of people involved, in the police and the CPS, deep down, think that as well. For another stabbing in a white community – like Clayton, which is also in my constituency – would joint enterprise have been used to this extent? I don’t think so.”

In his 2017 report on race in the criminal justice system, David Lammy MP stated that the government should adopt an “explain or reform” principle for racial disparities across the system.

What can explain the racially biased outcomes of joint enterprise? Does the requirement to speculate about the mental state – rather than simply the actions – of a defendant lead police, prosecutors and juries to assume the worst of certain people? “We always said in our research that the ‘why’ was racism,” Becky Clarke told me. “Understanding racism in its institutional forms, in its everyday forms, is fundamentally the ‘why’.”

Ben Crewe, one of the co-authors of the Cambridge study, is deeply concerned about the ongoing use of joint enterprise in light of its demonstrable racial disparity. The fact that one particular practice of the criminal law seems to so disproportionately target young black men – even more than the rest of the criminal justice system – “must tell us something very concerning about this society,” Crewe told me. “Something’s gone wrong somewhere along the line.”

For the young men in Moss Side and their families, the consequences have been devastating. Nathaniel Jermaine Williams, the driver of the Corsa, was sentenced to at least 19 years for murder. His brother cannot bring himself to explain it to his son, and has told him that Uncle Jermaine went to Australia to pursue his football career. Williams’s father, Remi, has suffered intense low moods. Durrell Ford’s mother will take a second job to cover the cost of travelling to County Durham to see her son in prison. Devon’ta Neish’s mother doesn’t know whether she’ll be able to travel to see her son at all. The mother of a 15-year-old sentenced to five years for manslaughter took months off her nursing job with stress, and still suffers from headaches and vertigo. Reano Walters, who will be at least 39 when he is released, is afraid he won’t be able to have children.

The youth worker Akemia Minott, who has known most of the defendants for years, is consumed by anger. “I don’t understand how they can justify themselves,” she said of the police and the courts. “It’s not a game. This shit’s not a game, this is real people’s lives. These lives aren’t less valuable than yours, these lives aren’t inferior to yours, or insignificant in comparison to yours. So why is the criminal justice system of a supposedly civilised and advanced country able to use certain people as just pawns in their game of chess?”

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