Five Thames Valley Police officers face manslaughter charges after a 24-year-old suspect who was arrested at a home in Milton Keynes died in hospital.
Brian Ringrose was taken to Milton Keynes University Hospital by ambulance after officers had medical concerns during his arrest on January 27.
The Independent Office for Police Conduct (IOPC) said the 24-year-old had been restrained using handcuffs and limb restraints and then carried to a police van in a 'flexible lift and carry system' (Flacs).
After being discharged from Milton Keynes University Hospital he was restrained by officers and taken to a police van to be transported to custody, before falling ill en route and being readmitted to hospital.
Mr Ringrose was then placed in an induced coma before dying in hospital on February 2 - with a post-mortem examination giving the cause of death as 'inconclusive pending further investigation'.
Five police officers have been told they are under investigation for alleged gross negligence manslaughter and unlawful act manslaughter.
Five Thames Valley Police officers face manslaughter charges after a 24-year-old suspect who was arrested at a home in Milton Keynes died in hospital. Stock image used
One of the officers is also being investigated for alleged common assault and all of them have been served with gross misconduct notices for potential breaches of professional behaviour related to use of force and duties and responsibilities.
An IOPC spokesperson said: 'The decision to inform officers they are under criminal investigation means evidence indicates a criminal offence may have been committed. This does not necessarily mean criminal charges will follow.'
IOPC regional director for the South East Graham Beesley said: 'Our thoughts are with Mr Ringrose's family and all of those affected by his tragic death.
'This is a significant development in our investigation and is based on evidence we have gathered to date.
Brian Ringrose was taken to Milton Keynes University Hospital by ambulance after officers had medical concerns during his arrest on January 27. Stock image used
'We have updated Mr Ringrose's family and will now seek to interview the officers under criminal caution.
'It is our role to independently investigate all of the circumstances when someone dies in police custody.'
Thames Valley Police has suspended its use of Flacs and the IOPC is looking at its use in other forces with the National Police Chiefs' Council.
A spokesperson for Thames Valley Police said: 'Our thoughts remain with Mr Ringrose's family at this very difficult time.
'We have been fully cooperating with the IOPC from the outset and will continue to do so. Support is being given to the officers involved.'