Police forces across England and Wales have been warned about the use of a type of restraint after a man died in custody when a belt was fastened across his face.
The Independent Police Complaints Commission (IPCC) said it had written to all chief constables across the country and "expressed concern" at the use of the emergency restraint belt as a spit hood because it "posed a risk to individuals".
The letter was sent following its investigation into the death of Thomas Orchard, 32, who died in hospital last year a week after being restrained by officers from Devon and Cornwall Police.
The force said its custody procedures were "constantly reviewed" and confirmed it no longer used emergency restraint belts as a spit hood or around the head.
The IPCC said it had passed files of evidence against the police staff who were involved in the care of Mr Orchard to the Crown Prosecution Service (CPS), which is now considering whether to bring charges.
"The IPCC identified a risk in the way that an emergency restraint belt (ERB) was used on Mr Orchard as a spit hood by Devon and Cornwall Constabulary and wrote to all chief constables in England and Wales on November 1 2012," the watchdog said in a statement.
"The letter expressed concern that use of an ERB in this way posed a risk to individuals. The IPCC highlighted the need for any other body using an ERB in such a way to carry out risk assessments.
"The IPCC investigation has concluded and has looked at CCTV footage, taken statements, interviewed officers and custody staff and reviewed relevant policies and training.
"The investigation has also looked at restraint techniques and the use of emergency restraint belts used by the force during Mr Orchard's arrest and detention."
Mr Orchard, a church caretaker who suffered from schizophrenia, was arrested on October 3 in Exeter city centre on suspicion of a public order offence.
He was later taken to the Royal Devon and Exeter Hospital when officers became concerned that he was not responding to them while in his cell. He died in hospital at 6pm on October 10 from suspected head injuries.
Mr Orchard's family said they had lots of unanswered questions about his detention.
"An emergency restraint belt was applied. We don't know how or why fully that it was applied. We have massive concerns about its use," Mr Orchard's sister Jo told Channel 4 News.
"We continue to ask questions to the IPCC and the CPS. We really need these questions answered."
Asked why the police would use the restraint on Mr Orchard, she replied: "Presumably they thought he might spit or bite. My family and I have never experienced him doing either."
In March, the IPCC recommended Devon and Cornwall Police suspend the six staff from their positions, although the force said it decided to only place them on "restricted duties" - meaning they were withdrawn from frontline service.
It said then that a file of evidence had been passed to prosecutors relating specifically to one officer during Mr Orchard's arrest and the level of force used.
A second file, which prosecutors received in July, focuses on Mr Orchard's time in custody and relates to two custody detention staff, three police officers, one custody sergeant and a nurse who is employed by a contractor.
"It will be a matter for the Crown Prosecution Service to determine whether criminal charges will be brought against any of those police staff involved in Mr Orchard's detention on that day," the IPCC said.
"The IPCC also submitted a file of evidence to the Health and Safety Executive (HSE) in August for them to consider corporate charges."
A Crown Prosecution Service spokesman said today: "We have received evidence from the IPCC in relation to the death of Thomas Orchard.
"We need to consider all of the current material in order to determine whether any further investigation is required.
"Once we are satisfied that we have received a full file, we will consider whether charges should be brought."
A spokeswoman for the HSE said it was reviewing the evidence it had been passed by the IPCC but was yet to launch a formal investigation.
"We are looking to establish what role there is for HSE in light of the IPCC's findings, but at this stage we have not launched a formal HSE investigation into Mr Orchard's death," a spokeswoman added.
Devon and Cornwall Police said the staff remained on restricted duties.
"Following this incident the force has assisted the IPCC wherever possible in gathering information regarding their inquiry," a spokesman said.
"An assessment was carried out by the deputy chief constable and it was decided the staff concerned remaining at work on restricted duties would not impact or prejudice the investigation in any way.
"It's important to note that no one has been criminally charged in relation to Mr Orchard's death and this investigation remains at an information-gathering stage.
"The staff concerned have been moved to temporary roles which do not have direct contact with the public and are outside of custody.
"This follows Home Office guidance around the suspension of officers.
"We now await further advice from the IPCC concerning any developments with potential prosecutions."
The force said that custody procedures were "constantly reviewed" and confirmed that emergency restraint belts were no longer used as a spit hood or around the head.
"Custody procedures are constantly reviewed as is any equipment used in the custody environment," a spokesman said.
"(The emergency restraint belts are being used) but not currently as a spit hood or around the head."