Two police officers who confronted an elderly disabled man with dementia at a care home by using a Taser, baton and incapacitant spray have been handed gross misconduct notices and are under investigation for manslaughter.
Questions are being raised over the use of force against 93-year-old Donald Burgess, who died several weeks later.
The Sussex Police officers were called to the care home in St Leonards-on-Sea, East Sussex, on the afternoon of Tuesday 21 June following a report that Mr Burgess had a knife and was threatening staff.
On arrival, staff at the care home showed the officers into a room where the man, who was in a wheelchair and had one leg, was holding a knife, the Independent Office for Police Conduct (IOPC) said.
Officers briefly engaged with the man, with one of the officers using PAVA incapacitant spray, followed by a baton.
The second officer deployed a Taser before the knife was removed from the man and he was handcuffed, according to the IOPC.
Mr Burgess was taken to hospital for treatment and remained there, where he died three weeks later on 13 July.
An IOPC spokesperson said: "Our investigation follows a voluntary conduct referral by the force on 28 June, concerning allegations of excessive use of force by the two officers who attended the incident.
"Gross misconduct notices have now been served on the two officers involved, both police constables, along with letters advising them they are under criminal investigation for manslaughter.
"These actions do not necessarily mean disciplinary proceedings or criminal charges will follow."
IOPC Regional Director Graham Beesley said: "I want to express my sympathies to the man's relatives and those who knew him. We have advised his next-of-kin of our independent investigation and explained the steps we will be taking.
"This will include investigating whether the force used by the two officers against this male, was reasonable, necessary and proportionate in the circumstances and in line with local and national policies, procedures and guidance."
Sussex Police Assistant Chief Constable Tanya Jones said: "We want to express our sympathies to the family and friends of Mr Burgess. Our thoughts remain with them at this difficult time.
"We are providing every assistance to the IOPC to allow for a thorough investigation and for the family to receive the answers they need."