The Independent Office for Police Conduct (IOPC) has confirmed it has launched an investigation into the incident in St Leonards-on-Sea in June.
The IOPC said police officers were called to the care home following reports that male resident Donald Burgess had a knife and was threatening staff.
On arrival, police were shown into a room where Mr Burgess, who was in a wheelchair and had one leg, was holding a knife.
IOPC investigators said the officers briefly engaged with Mr Burgess, then one of the officers used PAVA incapacitant spray on him.
The elderly man was then struck with a baton, before the second officer used a Taser stun gun on him, before the knife was removed and Mr Burgess was handcuffed.
The 93-year-old was taken to hospital following the incident for medical treatment. He remained in hospital where he died three weeks later.
The IOPC said its 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.
Initial steps carried out in the investigation have included taking witness statements and reviewing the officers’ body worn video footage.
An initial post mortem on 21 July proved inconclusive, and investigators are awaiting the findings of further cardio-pathology examinations.
Gross misconduct notices have now been served on the two officers involved.
Both officers, who are police constables,have also been served with letters advising them they are under criminal investigation for manslaughter.
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.”