One of the principal police officers involved in the restraint of a black man who died in custody has a history of violence and racism, it has been alleged.
Sheku Bayoh, originally from Sierra Leone, died after being arrested and restrained in Kirkcaldy in May.
The BBC has decided to name one of the officers involved, PC Alan Paton.
He is said to have attacked his parents and admitted to hating black people. He has not responded to the claims.
Bruised and battered
Mr Bayoh's family have now called on Police Scotland to explain why an officer with an apparent history of violence was allowed to be on independent patrol.
The BBC has obtained statements alleging that PC Paton, 41, carried out a sustained attack on his own parents at their home in 2005, while he was off duty.
The attack was said to have left his mother, Ann Paton, now 61, unconscious, and his father, John Paton, 65, severely bruised and battered.
Police officers from the then Fife Constabulary were called to the incident, but the BBC understands PC Paton's parents elected not to pursue a complaint, after being assured by senior officers the matter would be dealt with internally.
Barry Swan, 43, who is PC Paton's brother in law, told the BBC he had witnessed the aftermath of the alleged attack, and wanted to let the Bayoh family know about the police officer's past.
Mr Swan, who is married to PC Paton's sister, said: "What kind of person can actually do that to their own parents? Alan is a big boy, he towered over his mum and dad.
"A frail old man who'd basically been put through something he should never have been put through, he was literally black down one side. You knew instantly it wasn't one hit, he'd been kicked, he'd been stamped on. He'd had a major kicking."
Mr Swan also alleged that the officer had admitted to being racist in the weeks since Mr Bayoh's death.
He said: "He out and out admitted that he was a racist, that he hates them, as he puts it - all the blacks. It's not right he's a police officer."
Collette Bell, Mr Bayoh's partner and the mother of his eight-month-old son Isaac, said: "They're supposed to be trained in restraint. They should have the knowledge and ability to deal with those people appropriately without having to beat them to a pulp.
"There are ways and means to restrain somebody without killing them. There's no doubt about it, if Shek had not come into contact with the police he would still be here, and that hurts a lot.
"If somebody could beat up their own mum and dad why are they then left with the badge, why are they still allowed to patrol the streets?
"If they are that violent that they would hit out at their parents, what hope does any normal citizen have to go up against him?"
The Bayoh family lawyer, Aamer Anwar said: "I think the public have a right to expect that those who engage in violence and those who engage in racism should not be able to walk our streets as police officers. They must be held to account."
The death of Mr Bayoh is being investigated by the police watchdog, the Police Investigation and Review Commissioner (Pirc).
But Mr Bayoh's family has questioned whether it has the courage, powers or resources to properly hold Police Scotland to account.
How did Sheku Bayoh die?
Police had received a call on 3 May of this year about a man behaving erratically and brandishing a knife in Kirkcaldy.
The BBC understands that Mr Bayoh, who was a trainee gas engineer, had taken the drug ecstasy.
CCTV evidence seen by the family shows Mr Bayoh approaching the police at about 07:20. The BBC understands the pictures show that he did not have a knife.
At least two officers, including PC Paton, who until now has only been known as officer A, said that they believed they could be facing a terrorist incident.
At least four and up to six officers, including PC Paton, were immediately involved in the encounter.
CS spray and police batons were used and within about 30 seconds, Mr Bayoh was brought to the ground, face down. Handcuffs and leg restraints were applied.
PC Paton and a colleague known as officer B, who were two of the first on the scene, were understood to have a combined weight of about 43 stones.
Eyewitness reports suggested that officers were kneeling and lying on Mr Bayoh in order to restrain him.
Less than five minutes after the encounter began, Mr Bayoh was noticed to be unconscious and one officer radioed for an ambulance.
A further five minutes later, the ambulance still had not arrived, and an officer reported to base that Mr Bayoh was no longer breathing.
CPR was attempted by the officers, but Mr Bayoh arrived by ambulance at the town's Victoria Hospital, where his sister works, unresponsive. He was pronounced dead at 09:04.
A post-mortem examination revealed a series of injuries over his body, face and head, including a deep gash across his forehead.
Tiny blood spots, or petechial haemorrhages were discovered in his eyes - a sign of potential asphyxia.
The post mortem examination declared he had died after taking the drug MDMA, while being restrained.
But a report by a renowned pathologist engaged by the Bayoh family is expected to say the cause of death was positional asphyxia - effectively being suffocated as a result of the position his body was in.
Positional asphyxia is a common cause of death in police custody where restraint is involved.
This latest development in the Bayoh case comes just weeks after the resignation of Chief Constable Stephen House, who was criticised for visiting the officers involved in the restraint, including Alan Paton, before he met the Bayoh family.
His resignation came after a series of damaging incidents for Police Scotland.
Police Scotland Assistant Chief Constable Kate Thomson said: "It would be inappropriate to comment as there is an independent investigation into the circumstances surrounding Sheku Bayoh's death which is currently being carried out by the Police Investigations and Review Commissioner and they have submitted an interim report to the Crown Office.
"Police Scotland remains committed to co-operating fully with the Pirc's inquiries. I would like to again offer my condolences to Sheku's family and we await the conclusion of the investigation."
Pirc's ability to investigate independently has come under criticism after it emerged last month, in the Sunday Herald newspaper, that nearly three quarters of its senior investigators are ex-police officers.
The IPPC, the body which investigates police complaints in England and Wales came under similar criticism several years ago, and in 2013, the Home affairs select committee recommended that a maximum of 20% of IPCC staff should be made up of former police.
A Pirc spokeswoman said it was "exceptionally independent" from the police, and said "all relevant lines of enquiry were being pursued."
It also said that its staff had been recruited from a variety of background, including the police, fire service and military amongst others, for their skills in dealing with situations such as deaths in custody, crime-scene management and providing family liaison support.
The spokeswoman added: "It is not unnatural and is common in all police oversight bodies that a number of former, highly skilled and experienced former police officers are employed.
"Not only do such ex-police officers bring a high level of investigatory expertise to the job, they also provide a unique internal perspective on the policing system.
"We currently have 27 investigators, 12 of whom are from various non-police backgrounds."
The former head of the Scottish Police Federation Les Gray said he was confident Pirc would investigate circumstances surrounding the death of Mr Bayoh properly.
He told Good Morning Scotland: "There's nothing to suggest that Pirc are not going to do a good job, that they can't be relied upon. I am quite frankly baffled at the media coverage of this thing."
Bayoh family lawyer Mr Anwar has also alleged there was a smear campaign against Mr Bayoh in the days after his death.
He said: "The attempt to criminalise Sheku Bayoh in his death - the dead can't answer back but his family have answered for him.
"He wasn't 6ft plus, he was 5ft 10in. He wasn't super-sized, he was 12 stone 10 pounds. He wasn't brandishing a knife at a police officer. He didn't stab a police officer. In fact he wasn't carrying a knife when the police officers attended.
"He didn't attempt to stab anyone, and he wasn't found with a knife on him. Those are the actual facts."