A serving prisoner in a Westcountry jail has been arrested on suspicion of the manslaughter of an 89-year-old care home patient.
The 28-year-old man, who is being held at HMP Dartmoor on unrelated matters, is being questioned by detectives investigating neglect at Orchid View care home in Copthorne, West Sussex.
The arrest relates to the death in April 2010 of Jean Halfpenny, who was a resident at the care home.
A police spokesman said: "A Sussex Police investigation was launched last year examining neglect at the care home. The care home has since closed and reopened under a new name and new management."
In September and October last year, police arrested three people in relation to the investigation on suspicion of ill-treatment and neglect contrary to the Mental Health Act 2007 and the Mental Capacity Act 2005.
A 41-year-old woman from Crawley, along with a 55-year-old woman from South Godstone and a 49-year-old man from Burgess Hill, were bailed by police pending further inquiries.
The spokesman added: "The next of kin of all former patients who are subject of this investigation have been visited by Sussex Police."