A report by the Independent Police Complaints Commission (IPCC) said there was a series of missed opportunities by the health authority and police officers that took place in the run up to Rigg’s death.
The report follows a narrative verdict by a jury at Southwark Coroner’s Court, which found that officers used “unsuitable” force when restraining Rigg for eight minutes shortly before he died of a cardiac arrest.
Amerdeep Somal, who carried out the IPCC’s report, said: “Sean Rigg’s death is a symptom of a deeper problem: the linkage between mental illness and deaths in or following police custody.
“At the inquest, concerns were raised about the care Mr Rigg received from the South London and Maudsley Mental Health Trust (Slam).
“It is clear that, although staff at the supported hostel where he was living recognised that his condition was deteriorating during August and that his medication was overdue, he was not subject to a mental health risk assessment by staff at Slam.
“Nor did the police involved recognise or respond to his condition.”
Dame Anne Owers, chair of the IPCC, will now commission an external review of the watchdog’s original investigation, and an overall review of deaths in custody of the mentally in will begin in September.
Half of all deaths in police custody in 2011/12 were of people with mental illness, the report said.
“They represent a particularly vulnerable group, often, as in Mr Rigg’s case, failed by the people and systems that ought to protect them,” said Somal.
She added: “I have no doubt there are lessons for the IPCC from the investigation into Mr Rigg’s tragic death.”