The family of a Sierra Leonean man who died after being detained by up to nine police officers have demanded a robust independent inquiry after “grave concerns” emerged about police conduct surrounding the incident.

Sheku Bayoh, 31, died from suspected asphyxiation on a street in Kirkcaldy, Fife, on Sunday 3 May. He had been detained, handcuffed and put in leg restraints following an altercation with a female police officer and a colleague, and had been allegedly wielding a knife.

The controversy over has escalated after several conflicting and false accounts emerged about the incident, including the inaccurate allegation circulated to the media within hours of Bayoh’s death that the female officer might have been stabbed. It is understood pepper spray may have been used to subdue Bayoh.

The Bayohs’ family solicitor, Aamer Anwar, said he and the family had significant concerns about the investigation after he learned that none of the 11 officers involved in the case that morning had yet been suspended or interviewed by the independent Police Investigations and Review Commissioner (PIRC).

“Sensitive and thorough handling of the investigation in the ‘golden hours’ following the death is critical to evidence gathering and setting the direction and quality of the investigation to follow – the family has grave concerns with regards to what happened on Sunday,” Anwar said.

Anwar said the family, including Collette Bell, Bayoh’s partner and the mother of their infant son, were given five separate and contradictory accounts by police of what had happened over the 10 hours following his death.

“I want to know the whole truth of the circumstances surrounding his death so that one day I can explain to my son Isaac Bayoh, why he has had to grow up without his daddy,” she said.

Bell and Bayoh’s relations state they were being interviewed by police after his death but before the family was told he was dead. Bell, who had reported a burglary after finding their home in disarray, alleges that included interviews at their home by officers.

Bayoh’s sister, Kadijartu Johnson, a staff nurse also living in Kirkcaldy, told a press conference in Edinburgh the police had told her at 3pm that Sunday, six hours after her brother was officially declared dead at a nearby hospital, that a member of the public had found him lying on the street and they were looking for two apparent assailants.

“Several versions of events were given to my family for several hours after his death until finally we were finally told he had died in police custody in early evening,” Johnson said. “All we are asking for is the truth of what actually happened to my brother Sheku on the morning of Sunday 3 May.”

Speaking before he and Bayoh’s family met the lord advocate, Frank Mulholland, to raise their concerns, Anwar said he was shocked to learn that PIRC had not taken control over the case until Tuesday, and that it had no powers to suspend the officers involved.

Sheku Bayoh’s partner Colette Bell at a press conference in Edinburgh. Photograph: Andrew Milligan/PA

That meant the independent inquiry had lost valuable time in the first 24 hours to control the case and the witnesses.

“The family does not understand why the officers involved in engaging with Sheku Bayoh were not immediately suspended without prejudice after his death,” Anwar said.

“It is a matter of wider public concern that officers remain at their desks or in contact with the public pending the outcome of the investigation into a death in custody. For the chief constable to suspend the officers without prejudice is not a question of pre-judging the outcome of the investigation but ensures neutrality, integrity of the investigation, transparency as well as protecting officers involved in such incidents.”

Johnson said her younger brother had moved to the town when he was 17 to be near her. “He had grown up to be a hard working father, who lived for his two boys and was always so proud of them and loved his partner Collette,” she said.

“At this point in time our family is heartbroken, not able to grieve; his body is still in the mortuary all alone. Even once we have buried my baby brother we will not be able to grieve until we know the truth.”

Anwar said the high commissioner of Sierra Leone, Edward Turay, had also expressed concerns and was due to travel to Scotland to meet the family and seek a meeting with the lord advocate as Bayoh was still a Sierra Leonean national.

He refused to discuss the exact circumstances surrounding Bayoh’s arrest or why the police tried to detain him, insisting those were matters which had to be independently verified by PIRC after the police and witnesses were properly interviewed. It is understood the incident has been captured on nearby CCTV cameras.

But Brian Docherty, chairman of the Scottish Police Federation, which represents rank and file officers, insisted that Bayoh had presented a physical threat to the officers involved. Docherty said he regretted that Anwar was “making unhelpful comments to the press” and said he did not like “innuendo and speculation” about the case while the PIRC investigation was under way.

Docherty added, however: “A petite female police officer responding to a call of a man brandishing a knife was subject to a violent and unprovoked attack by a large male.

“The officer believed she was going to die as a result of this assault. I very much regret that Mr Bayoh sadly lost his own life following this incident but innuendo and speculation whilst the independent investigation is ongoing adds nothing other than to the pain and grief of the family.”