Warren Fenty, 20, died in a cell in Kittybrewster Police Station following a methadone overdose in 2014.

The FAI into his death found it was “likely” avoidable.

Sheriff Principal Derek Pyle found that “no one individual can be held responsible” for the tragedy but did detail failures of Police Scotland and the care Mr Fenty received.

Mr Fenty suffered fatal methadone intoxication on June 29 2014 at 7:25am. He had earlier been arrested at Aberdeen Royal Infirmary after discharging himself – against the advice of the doctor who had treated his overdose.

“In my opinion, there were a number of institutional failures by Police Scotland, which while not material as a contributory cause of Mr Fenty’s death were nevertheless precautions which if they had been taken would have presented opportunities for Mr Fenty to be returned to hospital,” Sheriff Principal Pyle said.

He said that such intervention “would have probably resulted in clinicians realising at some uncertain point in the hours before his death that Mr Fenty’s life was at risk and would have been able to prevent it”.

He also criticised custody officers who failed to follow the rules on conducting cell checks, “which created a missed opportunity which might have resulted in them seeking the advice of the forensic medical examiner, which might, in turn, have resulted in Mr Fenty’s re-admission into hospital, which might have avoided his death”.

Working conditions at the custody suite, which was new at that time, were “chaotic”, with only two officers “running around like headless chickens” as they looked after 42 prisoners.

The sheriff principal said: “It was always likely that such officers… would struggle to cope.”

Sheriff Principal Pyle said: “In my opinion, it can be concluded that if Kittybrewster had been run properly and DVR compliant checks had been performed, it is possible that medical assistance would have been sought for Mr Fenty, that he would have been returned to hospital and that he would have survived.”

The Crown Office also came in for criticism, having taken five years to investigate the death. Sheriff Principal Pyle noted that only two of those years were “usefully spent”. There was a three-year gap of inactivity that he said “cannot be excused”.