This feature was updated on 18 January to reflect developments in the case.
It's about 07:20 on a Sunday when the first two police officers arrive. They're responding to 999 calls of a black male carrying a knife.
The young man is disorientated, wandering. He's behaving erratically, and looks like he could be drunk or high on drugs.
The officers bring their van to a rapid stop directly in front of him, the sirens and their shouts piercing the quiet morning.
He no longer has a knife and appears to be walking away, but two more officers arrive. They draw their batons and irritant sprays; they use them.
Within 45 seconds the man is taken to the ground, struggling, as more officers arrive.
A total of nine uniformed officers are soon on the scene.
A witness sees up to six policemen kneeling and lying across the man, and hears him shout: "Get off me."
By the time the officers do get off, it's too late - he is unconscious. The officers begin resuscitation.
It is less than five minutes since the police arrived, and Sheku Bayoh is dying on the pavement, with his hands and legs bound.
He never gets back up.
Ninety minutes later, the 31-year-old father-of-two is pronounced dead in hospital. His body bears 23 separate injuries.
'Your brother is dead'
On 3 May, 2015, Kadi Johnson, a nurse at the local hospital in the town of Kirkcaldy, was going about her day.
She didn't have a shift at the hospital that day, but had also been working as a part-time home carer, and had been to see a local client.
She was tired, and decided to get back into her pyjamas. At about 15:00 she was in the kitchen, chatting and preparing food with a relative when the doorbell rang. Her husband Adie answered.
Two detectives were at the door. They had information about her brother.
Sheku, they told her, had died that morning.
"I had just seen him the night before at a family party for my daughter's birthday. He was well, he was fine. I was shocked. But the officers wouldn't tell me anything about what happened.
"At first they told me he'd been found on the ground. Then they said they were looking for two men. Eventually, after talking to their boss, they told me there had been a forceful arrest, and he'd died on the way to hospital. We just couldn't get a straight answer out of them."
Answers are what Kadi has been looking for, for the past five years. She has been at the forefront of a high-profile campaign to establish the truth around the circumstances of Sheku's death at the hands of police officers.
Recent events in the US have thrust the campaign back into the spotlight, as comparisons have been drawn with the death of George Floyd, who died in Minneapolis in May as a white police officer held a knee on his neck.
The family of Sheku Bayoh are pinning their hopes on a judge-led public inquiry, the terms of which were announced in May.
It will be the first in Scotland to examine a death in custody, and will investigate if Sheku's "actual or perceived race" played a part in events leading up to and after his death.
The death of George Floyd 'just brought it all back'
The town of Kirkcaldy in Fife lies on Scotland's east coast. It has a population of some 60,000, and like much of Scotland's industrial heartlands has suffered economic decline in recent decades. One in five families there live in poverty.
It is far from ethnically diverse. The 2011 census showed more than 97% of the town's residents were white and just 1% black.
This was the town that Kadi chose to make her home two decades ago.
Originally from Sierra Leone, West Africa, she had settled in the UK in the 1990s. She moved from Coventry to Kirkcaldy to study nursing.
Kadi says she was so taken with how beautiful and safe Scotland was, she suggested her younger brother Sheku join her. He had been living in south London since 1995, when he arrived as a 12-year-old unaccompanied minor seeking to escape the civil war in the country of his birth.
Not especially academic, Sheku was keen to leave school and get into the real world, and jumped at the chance to move north. He arrived in Kirkcaldy in 2000 aged 17, ready to start his new life.
A number of jobs beckoned, including an apprenticeship with Fife Council and a position in the local branch of DIY chain B&Q.
He was involved in the community, a youth leader with a local racial awareness group. He even gave talks to the local police about the issues faced by the minority ethnic youth of Kirkcaldy.
Sheku was granted the right to live in the UK permanently in 2008.
By 2015, he was a trainee gas fitter with Scottish Gas. He had settled down with his partner Collette, and Kadi says he'd been "over the moon" when their baby, Isaac, was born.
He had another son, Tyler, from a previous relationship, whom he saw regularly.
"He just lived for his children really," says Kadi. "The short time he had with Isaac was, I'm sure it was his best time. He enjoyed every moment of being a father."
But Kadi's decision to send for her brother all those years ago now haunts her.
"That is the guilt that will live with me until the day I die," she says.
Sheku Bayoh is not George Floyd and Kirkcaldy is not Minneapolis, but there are striking parallels in both these deaths.
Once again questions are being asked about how black people are policed and, when they die after contact with the state, how justice is served.
The recent protests in the UK and in the US have been fuelled by the video capturing George Floyd's dying moments.
"I could not watch it," says Kadi, now 42. "Too painful. It has brought back so many memories of how we felt in 2015. It seemed like my brother. It just brought it all back.
"George was quickly put down on the ground. Same like Sheku."
An initial autopsy suggested underlying health conditions and intoxicants could be to blame for Floyd's death, and there was nothing to support a diagnosis of asphyxia. A second autopsy commissioned by Floyd's family flatly contradicted this, concluding he died of asphyxiation due to neck and back compression.
"Again, the same as Sheku," says Kadi. "The authorities here wanted to blame it all on the drugs he'd taken. We don't condone his taking drugs, but he was not himself.
"And we believe that if Sheku was white, he would have been treated differently and still be alive today.
"When a black man dies at the hands of police, they always try to blame it on him, blame anything but those responsible. We're tired of this now. It is enough.
"This time, they chose the wrong family."
'This is what happens to black boys with big mouths'
The death of Sheku Bayoh was to become Scotland's most high-profile death in police custody.
Like in the US, the UK's racial pressure points often occur as a result of treatment of black people by the police.
The watershed public inquiry into the Metropolitan police's handling of the murder of Stephen Lawrence - the teenager killed in a racist attack by a gang of white youths in Eltham, south-east London in 1993 - found the investigation into Stephen's murder, and the force itself, was institutionally racist.
It is a label that has hung heavily on not just the Met, but forces across the UK ever since.
In the case of Sheku Bayoh, all of the officers involved in his death were white.
Just 1% of Police Scotland's officers and staff identify as being from an ethnic minority background, compared with 4% of Scotland's population as a whole.
From the outset, the Bayoh family wanted to know if race had played a role in Sheku's death.
The family quickly instructed prominent human rights and criminal defence lawyer Aamer Anwar.
His own experience had been formative. In 1991, while a student in Glasgow, he was badly beaten by a police officer in a racist attack, resulting in two of his front teeth being knocked out. Barely conscious, he heard an officer say: "This is what happens to black boys with big mouths." He sued the police and won, making Scottish legal history.
Eleven days after Sheku Bayoh's death, Mr Anwar organised a press conference. In front of the media, Sheku's partner Collette Bell fought back tears, saying she would not rest until their child Isaac, then only three months old, knew why he was growing up without his father.
Kadi and Mr Anwar also spoke about the need for the Police Investigations and Review Commissioner (Pirc), the body which investigates deaths in police custody in Scotland, to get to the bottom of the case.
Within hours, the Scottish Police Federation, the organisation which represents rank and file police officers of Scotland's national police force, was also talking to the media.
The federation's lawyer told them that "…a petite female police officer was … subjected to a violent and unprovoked attack by a very large man who punched, kicked and stamped on her [and that she] believed she was about to be murdered."
Reports followed in the press describing Sheku as a "dangerous man, armed with a large knife, crazed on drugs", leaving officers fearing for their lives.
The reports stressed his supposed size, while the small stature of the female officer was also emphasised.
"From the beginning, the family refused to speculate on what happened and wanted Pirc to carry out a robust investigation," says Mr Anwar.
However, officers involved in the restraint of Sheku had been advised by the Federation not to give statements to the Pirc, leaving investigators and Bayoh's family without key information.
It would take three years before the lord advocate, the most senior prosecutor in Scotland, decided there would be no prosecutions against any of the nine officers involved in the events of that morning in May 2015. The "evidence would not currently justify criminal proceedings," a spokesman said.
"We felt completely betrayed," says Kadi. "It was like his death didn't matter. But we had to keep going. People need to know the truth. Sheku's children deserve to know the truth."
The campaign shifted focus to persuade the Scottish government to hold a public inquiry.
'He wasn't himself'
On the day of his death, Sheku had been at the home of a close friend, Martyn Dick.
The pair had known each other since 2006.
"He and I just clicked very quickly," Martyn told the BBC in 2018.
"We'd a lot of things in common, just really bounced off each other, enjoyed each other's company. It was hard not to be attracted to his personality. He was a real people person, to be honest. I've described him before as a friend to everyone.
"His accent was unique - a broad mixture of Scottish slang, London and a bit of African as well. It was like nothing else I've ever heard. It was one of the most unique things about him."
Martyn says Sheku was known to walk away from fights, and did not have a reputation for violence.
"I never saw him raise his voice let alone his hands," he said. "He was just not that kind of guy. He would never let his temper flare or anything like that. That wasn't his nature at all."
Martyn was also one of the last people to see Sheku alive. He said he knew that Sheku occasionally used recreational drugs, and thought he probably had taken something when Sheku arrived at his house early on the morning of 3 May to watch a boxing match.
"He wasn't himself. He just seemed confused and the atmosphere was strange because we couldn't get through to him. So he decided it would be better for him to leave and he said sorry.
"I thought he's going to go home and everything will be fine tomorrow."
Toxicology reports would later show that Sheku had taken MDMA and another hallucinogenic drug called flakka.
Sheku walked the few streets to his own house, escorted by another friend, but by then his behaviour was dramatically altered by the drugs he'd taken. He then attacked his friend, and the friend left.
Just before 07:00, Sheku took a knife from his kitchen, and went outside. It was at this point, worried residents saw him wandering the streets and called 999.
It set in motion a chain of events that would ultimately lead to his death.
'He's not running away'
Following the decision not to prosecute any of the officers involved in the death of Sheku Bayoh, BBC Scotland's Disclosure programme started investigating. We obtained documents and video evidence at the heart of the case.
Using the police officers' own testimony, as well as eyewitness accounts and CCTV, we were able to piece together the events of that morning.
The revelations in the film, broadcast in December 2018, cast new light on the accounts given by the officers.
Some had said they were in fear of their life from Sheku. The officers' own statements revealed Sheku no longer had the knife, although some said they feared he may have concealed it. The knife was found later, in a nearby garden.
The documents also revealed that within 30 seconds of encountering Sheku, three officers discharged their irritant spray into his face, and batons were used, even though Sheku had not been violent towards them.
The CCTV appeared to show Sheku retaliating and chasing a female officer, knocking her to the ground. The officer, later named as PC Nicole Short, had injuries consistent with being hit on the head.
In her statement, she said: "I felt an almighty blow to the back of my head… it knocked me flying towards the ground.
"I was in the foetal position… I thought, 'This is it, he's going to kill me'."
We asked a leading authority on police restraint and use of force, Eric Baskind, of Liverpool John Moores University, to analyse the material.
In the 2018 film, Mr Baskind said: "What strikes me from the evidence of the officers is that they approach the scene with the intention of using force.
"He [Sheku] is not running away, he's not, at that moment in time, creating a danger to anyone. They get there, they screech to a halt, they get out of the cars with irritant sprays and batons.
"Those actions were very escalatory. And once you ramp things up to a certain degree it is very difficult, if not impossible, to backtrack."
Mr Baskind said this could have been prevented, if the officers had approached the situation differently, in line with their training.
"What we can't rule out is that Mr Bayoh is going through a mental health crisis, and from his perspective, he might have seen the discharge of the irritant sprays, the baton attacks, as him being attacked.
"Had they approached Mr Bayoh in a different way, in a calming way, to try and find out what was wrong, then in my view, that attack may have been prevented."
What of the police officers' version of events?
On the advice of the Federation, the officers did not speak to investigators for 32 days, being advised to wait for the results of toxicology reports into what substances were in Sheku Bayoh's system.
In their statements, each officer was identified by a letter to preserve their anonymity - although two have since been identified.
Multple references were made of Sheku Bayoh's size and strength.
Officer A said: "I cannot emphasise the strength of this guy."
Officer E said: "He was massive and is the biggest male that I have seen."
But Sheku Bayoh wasn't even the biggest male there that day.
Sheku was a muscular 5ft 10in, weighing 12 stone 10lb.
Officer A was 6ft 4in, of proportionate build.
Officer B was also 6ft 4in and 25 stone.
It was also claimed by the Scottish Police Federation that once PC Short was on the ground, Sheku viciously stamped on her.
This was based on the testimony of officers B and C.
Officer C's statement said: "He stomped on her back with his foot with a great deal of force. He put his full bodyweight into the stomp and used his arms to gain leverage."
PC Short, was taken to hospital for a check-up, and returned to the police station shortly after.
In her statement, PC Short did not say she was stamped on. There was no mention of it in the statements of three witnesses who saw the incident.
The CCTV casts doubt on this claim. As soon as PC Short was knocked to the ground by Sheku, the action immediately moved elsewhere, and Sheku was confronted by the other officers. Within five seconds, he was brought down, never to get back up.
Mr Baskind said: "The quality of the footage is not very good, but you can certainly make out what's going on, and I can see no evidence at all of two stamping attacks on the officer on the ground.
"There certainly seems to me to be a significant discrepancy between what I can see on the footage, and what I've read in the papers."
New allegations over this apparent discrepancy were revealed in a BBC Panorama programme in January 2021.
Kevin Nelson was an eye witness to the altercation between Pc Short and Sheku, and saw him react to be being sprayed by punching the officer to the ground. But there, he says, the altercation finished and he was intercepted by the other officers.
"He was running off," he said. "After the punch, that was it. There was no more attack on her at all."
Asked about the officers' claims of a violent stamping attack on Pc Short, Kevin told the programme, "That never happened."
"It's not fair on Sheku and his family that [the officers] made the incident worse than it actually was to justify what had happened. That's not right.
In response, the Scottish Police Federation said its officers had cooperated truthfully with investigators, and it had seen compelling "compelling material" the stamping attack had taken place.
When asked to provide this, the federation said the "proper forum" was the public inquiry.
The BBC had previously obtained mobile phone footage of the restraint.
Officer B told investigators he had Sheku pinned to the ground for "a maximum of 30 seconds". Another officer said the restraint had been, "appropriate, text book stuff, in line with their training".
A civilian witness saw it differently. She told investigators around six officers were lying across Sheku for several minutes.
She said: "I heard him screaming. It sent chills through me. I heard the man shout to get the police off him. They never moved."
Nine officers were involved at different times in the restraint, in which handcuffs and leg restraints were used.
The image above appears to show Officer B, who weighed 25 stone, lying across Sheku.
Around four minutes after the restraint began, Sheku fell unconscious, and an ambulance was called. The officers attempted resuscitation. He was taken to the nearby Victoria Hospital - the same hospital his sister Kadi worked at - where he was pronounced dead.
Sheku suffered 23 separate injuries, including a cracked rib, head wounds consistent with baton strikes, and petechial haemorrhages, or burst blood vessels in the eyes, which can be a sign of positional asphyxia, or suffocation.
The official cause of death was noted as "sudden death in a man intoxicated… [with drugs] whilst under restraint."
The Federation says that Sheku Bayoh's race played no part in his treatment that day.
The Disclosure programme revealed that two of the officers said they feared they were under terrorist attack, referencing the murder of soldier Lee Rigby, stabbed to death two years earlier on a street in Woolwich, south-east London, by two extremists, Michael Adebolajo and Michael Adebowale, who were black.
Another female police officer, Officer E, used the word "coloured" - a term considered to be outdated and offensive - to describe Sheku in her statement.
She said "[as we approached] I was also thinking at that point of the Lee Rigby incident in London, mainly due to the fact of the coloured male and the potential terrorist connotations."
The UK terror threat level was at "severe", as it had been for the previous eight months.
Eric Baskind told the BBC, "If they genuinely believed that they were coming into a terrorist incident, I would've expected them to have called that through to Control."
No such call was made.
"It's the question that family have always asked: 'Why, when you see a black male walking down the street, does the word "terrorist" come to mind?'" says Aamer Anwar. "It's Kirkcaldy, it's Sunday morning, it's half past seven. Seriously?
"This isn't London. It's not Westminster Bridge. Why did the police officers believe they were under a terrorist attack?"
The suspicions of Sheku Bayoh's family that race played a part in his death were further fuelled when Officer A, PC Alan Paton, was revealed by the BBC to have been previously accused of hating black people.
Family members alleged Paton had confessed to being racist in the weeks following Bayoh's death.
PC Paton has since retired from the force on medical grounds and his lawyer told the BBC he will not comment ahead of the inquiry.
PC Nicole Short has also retired on medical grounds.
More than 1,000 people have died in police custody in the UK over the past 30 years.
In those deaths where restraint was a factor, the person was twice as likely to be black, Asian or minority ethnic.
No officer has been disciplined as a result of Sheku Bayoh's death. No criminal charge has ever been brought.
"That's where the similarities between Sheku and George Floyd's case ends. Four officers face trial for George. No-one will face trial for Sheku," says Anwar.
The 2018 Disclosure film prompted renewed calls for a public inquiry, and less than a year later, Scottish Justice Secretary Humza Yousaf announced that one would be held into the death of Shaku Bayoh.
The Scottish Police Federation has insisted race played no part in Sheku's death, suggesting instead "the drugs in his system is more relevant."
That now will be decided by the public inquiry, led by retired judge Lord Bracadale, whose terms of reference include investigating whether Sheku's "actual or perceived race" played a part in events.
The inquiry is now under way and is expected to last several years.
The Scottish Police Federation told the BBC it would be "entirely inappropriate" to comment on the case.
It said that the BBC had presented questions based on "inaccuracies, falsehoods, hypothesis and speculation which we will address through [the] public inquiry, not through the media."
Chief Constable Iain Livingstone told us, "The death of Sheku Bayoh was, and remains, a terrible tragedy. It has had a traumatic impact on his family and friends, as well as affecting many people within policing and the wider community of Kirkcaldy and Scotland.
"I am committed to supporting all those who have been affected by Sheku Bayoh's death throughout this time.
"I met privately with the family of Sheku Bayoh in December 2019 and expressed to his mother and sister my sincere personal condolences, and those of the service. I also undertook that Police Scotland will participate fully in the public inquiry in an open and transparent manner.
He added, "It is vital that the role and independence of the public inquiry is respected to ensure the application of the rule of law, due process, and justice being served."
A £1.85m civil claim by the family against Police Scotland has been temporarily halted, pending the inquiry.
Sheku Bayoh had broken the law that morning and the Bayoh family do not dispute that the police, responding to emergency calls, had to act.
But they also maintain Sheku was in the grip of a mental health crisis and needed help. If he had to be arrested, he had a right to be arrested safely, they say, with proportionate and not deadly force.
"We are always hopeful people will understand that my brother was not a bad person," says Kadi. "He was a good man who cared for his family and friends. We want the public to know that.
"His children deserve to know how their father died. That's what keeps me going."
Watch on BBC iPlayer: