Two police officers involved in the death of a black man they were restraining may have provided false statements, the BBC can reveal.
They said Sheku Bayoh carried out a stamping attack on a female PC before he was brought to the ground and restrained by up to six officers.
But now an eyewitness has spoken publicly for the first time about the 2015 incident.
He told a Panorama investigation that the stamping attack "never happened".
The Scottish Police Federation said its officers had cooperated truthfully with investigators.
Mr Bayoh, a 31-year-old father of two, died in the incident in the Fife town of Kirkcaldy in 2015.
A public inquiry into the circumstances surrounding his death has recently got under way. One of its tasks is to examine whether his race was a factor.
On the night of 2 May 2015, Sheku Bayoh had taken drugs, which friends said dramatically altered his behaviour.
Police were called early the following morning after he was spotted behaving erratically with a knife in the streets of his home town.
According to police statements, by the time the officers arrived at the scene Mr Bayoh no longer had the knife but he failed to obey instructions to get down on the ground.
Each of the officers used force on Mr Bayoh within seconds of encountering him, including CS Spray and batons.
He then punched PC Nicole Short, who went to the ground.
Two officers, PCs Craig Walker and Ashley Tomlinson, would later tell investigators that Mr Bayoh then carried out a violent stamping attack on PC Short while she lay on the ground, a claim reported widely in the media.
PC Walker told investigators: "I had a clear view of him… he had his arms raised up at right angles to his body and brought his right foot down in a full-force stamp on to her lower back."
PC Tomlinson said: "I thought he had killed her. He stomped on her back again."
Now, evidence obtained by Panorama suggests these accounts may be false.
Mr Bayoh was restrained on the ground for five minutes before falling unconscious. He was pronounced dead at hospital a short time later.
A post-mortem examination report revealed 23 separate injuries to Mr Bayoh's body, including a broken rib and gashes to his head. The cause of death was recorded as "sudden death in a man intoxicated [with drugs] whilst under restraint".
In 2018, the Crown Office in Scotland decided there would be no prosecutions against any officers involved.
The new evidence
Kevin Nelson was in a nearby house and saw events unfold over a garden hedge.
He gave his account to investigators from Pirc (Police Investigations and Review Commissioner), which investigates deaths in custody, two days after the incident.
Speaking publicly for the first time, Mr Nelson told Panorama he saw Mr Bayoh attempt to walk away from the officers, ignoring their commands, before being sprayed with CS spray. He said Mr Bayoh retaliated and punched PC Short.
Asked if there had been any further contact with PC Short, he said, "No. He was running off… after the punch, there was no more attack on her at all."
Mr Nelson said Mr Bayoh ran off from where PC Short went down and was quickly intercepted by the other officers.
Asked about PC Walker's claim that Mr Bayoh had "his arms raised up… and brought his right foot down in a full force stamp", Mr Nelson said: "That never happened. I didn't see him stamping at all or, other than the punch, any raised arms.
"After the punch, that was it. There was no more attack on her at all. That's not right."
The officers provided their accounts to investigators 32 days after Mr Bayoh's death.
Mr Nelson said no-one from Pirc returned to ask about the discrepancy between their account and his.
The eyewitness said he decided to speak out because it was unfair on Mr Bayoh's family that the officers had "made the incident worse than it actually was to justify what had happened and… that's not right".
Mr Nelson's account is supported by CCTV footage of the incident, obtained by the BBC.
It is poor quality but appears to show that once PC Short is knocked down by Mr Bayoh, the action moves away from her, and he is brought down within five seconds.
PC Short did not mention in her statement she had been stamped on. Now retired, she later said she was unsure if she was conscious, and only learned about the alleged stamping attack when her colleagues told her about it afterwards.
In the CCTV, PC Short appears to get to her feet a few seconds after Mr Bayoh is brought down.
Mike Franklin, former commissioner for the body which investigated police complaints in England and Wales, looked at Panorama's evidence.
He said: "I think there's nothing more serious than a police officer who gives false information in an investigation where somebody has died. So without accusing them of lying, I simply say that there's a big conflict.
"Two officers who were there say that it did happen. The person to whom it happened didn't mention it. And an eyewitness says it didn't happen.
"I would've been reluctant to sign off the investigation as complete, without resolving those… conflicts of evidence."
Mr Bayoh's sister, Kadi Johnson, told Panorama the new allegations had made her "really angry".
She said the way her brother was "painted" by the accounts given after his death was not who he was.
A spokesman for the Scottish Police Federation, which represents rank and file officers, said serving officers were unable to comment on matters "to which they may be called upon to give sworn evidence" but that they had "co-operated fully and truthfully with the investigations that have taken place".
It added it had seen "compelling material that Mr Bayoh did violently stamp on the back of a policewoman as she lay unconscious".
The BBC asked for this material to be produced but was told the inquiry was the "proper forum" for such matters.
The Crown Office, which directed the Pirc Inquiry, told Panorama it had examined "eye-witness accounts of police and civilian witnesses" and instructed "appropriate investigation".
It said after careful consideration it was decided there should be no prosecutions but reserved the right to prosecute should evidence become available.
Pirc told Panorama its investigation was "detailed and extensive" but could not comment further because of the public inquiry.
Police Scotland Chief Constable Iain Livingstone expressed his condolences to the Bayoh family and said the force would "participate fully" in the inquiry.
Panorama's "I Can't Breathe: Black and Dead in Custody" also investigates the case of Kevin Clarke, 35, who died in 2018 after being restrained in London by up to nine officers.
An inquest into his death resulted in a damning verdict on the police and ambulance services.
Mr Clarke's sister Tellecia told the programme that if the officers "hadn't used excessive force he would still be here today… treat him like a human being, and not just see him as a big scary black man".
Metropolitan Police Commander Bas Javid apologised to Mr Clarke's family and accepted the restraint had not been appropriate.