A watchdog is investigating claims that Avon and Somerset police officers lied during an inquest into the death of a mentally ill man.
The Independent Police Complaints Commission (IPCC) has served five Avon and Somerset staff - including three serving police officers - with notices of gross misconduct over the death of 25-year-old James Herbert.
The former public schoolboy died from a cardiac arrest in June 2010 after being detained under the Mental Health Act by officers from Avon and Somerset Police.
An inquest last year heard that Mr Herbert, who had taken drugs, was restrained before being left naked in a police cell at Yeovil police station.
Mr Herbert, a data recovery engineer, was later found to be unresponsive and was taken to Yeovil District Hospital by ambulance where he was declared dead.
An inquest jury returned a narrative conclusion that Mr Herbert, who lived in Wells, died from "cardio-respiratory arrest in a man intoxicated by synthetic cathinones causing acute disturbance following restraint and struggle against restraint".
The jury also highlighted factors that may have contributed to Mr Herbert's death, such as the lack of communication between police officers about Mr Herbert's mental health, drug use and previous incidents; the failure to call for medical assistance while he was being taken to the police station and the need for closer monitoring of him during that journey.
The police watchdog said it was looking at "whether the police at any stage colluded to give false accounts and/or lied during their evidence at the inquest".
A spokeswoman said: "Following the inquest into the death of James Herbert, Avon and Somerset Police received a letter from Mr Herbert's family detailing a number of complaints including concerns that officers colluded or lied during their evidence, and about the conduct of the force during the inquest proceedings.
"These complaints were referred to the IPCC which decided to carry out an independent investigation.
"The IPCC has looked at the evidence provided to the IPCC as part of the original investigation into Mr Herbert's death.
"A number of areas relating to the treatment of Mr Herbert on June 10 are now being investigated further.
"As well as investigating whether the police at any stage colluded to give false accounts and/or lied during their evidence at the inquest, the IPCC is examining the actions and decisions of police officers or staff who had any involvement with James on the day of his death."
Three police officers, one former police officer and one member of police staff have been served with gross misconduct notices advising them that their conduct is subject to investigation.
"The notices relate to the investigation into the circumstances of Mr Herbert's death. Such notices are not judgemental in any way," the spokeswoman added.
The jury in an inquest into the death of a man who died in police custody is continuing its deliberations today. James Herbert, 25, died at Yeovil Police Station three years ago.
He'd been detained in Wells hours earlier under the Mental Health Act. There had been numerous calls to police about his behaviour in the city.