THE body charged with investigating the police in Scotland has denied it is seeking to blame a controversial medical condition for the death in custody of Sheku Bayoh.

The Police Investigations and Review Commissioner (PIRC) has submitted its initial findings on the case to Lord Advocate Frank Mulholland, including a report commissioned from US-based experts in "excited delirium".

The condition has been blamed by police forces in America and England for previous deaths in custody and is said to involve a delirious person showing symptoms including anxiety, hallucinations, violent behaviour and “superhuman” strength.

Mr Bayoh's family's lawyer Aamer Anwar said the family has been waiting 17 weeks to establish the cause of death and had lost confidence in PIRC's ability to properly investigate Police Scotland.

Ahead of a meeting with the victim's family this week, PIRC commissioner Kate Frame said instructing pathology experts from outwith Scotland was not a sign it had "focused its investigation on a particular cause of death for Sheku Bayoh".

She added: "The post mortem conducted in Scotland did not reveal a conclusive cause of death.

“In order to assist the family in understanding what caused Sheku Bayoh’s death, PIRC identified a number of expert forensic pathologists to the Crown Office.

“The Lord Advocate then selected and instructed the Commissioner to approach the chosen experts and seek their opinion on the cause of death.

“Both are entirely independent. Once the experts’ opinions are available they will be passed to the Crown Office and the PIRC would anticipate that, in accordance with standard practice in a serious case such as this, they will take the opportunity to precognosce them as witnesses along with other significant witnesses identified in the PIRC report."

Claiming there were "glaring gaps" in the probe to date and comparing the case to the Glasgow bin lorry crash, Mr Anwar also said the Crown Office could not rush to close off any avenue of inquiry.

Mr Anwar said: “It would appear that for PIRC, the central question became one of whether Sheku died from some mysterious syndrome as opposed to excessive use of force by the police.

"We need to learn from the bin lorry crash and the Chief Constable's recognition that victims' families will no longer be silenced and that robust investigations need to be carried out.

"For the cause of death not to be determined after 17 weeks is simply unacceptable. The Lord Advocate retains the confidence and faith of the family because he said that he will look at other experts, take on suggestions and look at all options. But that confidence isn't blind."

But one policing source said that while excited delirium had to be examined as a possibility it was unlikely to have been a factor, pointing to tests which are understood to have revealed the presence of the drug ecstasy in Mr Bayoh’s body.

The source added: "I'm 1000 per cent confident that the Fatal Accident Inquiry will reveal any injuries to be in line with a standard police arrest."

Mr Bayoh, a father who worked for British Gas, died on May 3 after being restrained by several officers who responded to a call out on a Kirkcaldy street.

He did not have a knife when he was approached by officers. One is said to have been found nearby later.

It is understood he was handcuffed and put in leg restraints following an altercation with the officers. He died in custody after losing consciousness.

Within twenty-four hours, PIRC was instructed by the Crown Office to investigate the circumstances of the death.

A further report yesterday detailed the extent of injuries Mr Bayoh sustained, including a broken rib and the presence of petechial haemorrhages in his eyes, a recognised symptom of asphyxiation.

A Crown Office spokesman said: “The Crown will take the PIRC report into account when carrying out their own investigations."