Police in Norfolk say an allegation has been made about the care a patient received at a Norwich hospital before he died.
A man in his late 40s, who had been receiving treatment at Hellesdon Hospital, had a medical emergency on Tuesday 1 October.
He was taken to the Norfolk and Norwich University Hospital, where he died three days later.
Detective Chief Inspector Tracey Little said the allegation related to "the care the patient received prior to and during the medical emergency" at Hellesdon Hospital.
"A Home Office post-mortem examination has been carried out but proved inconclusive and further tests will now be carried out," she added.
The death is being treated as unexplained.
Police said the investigation was not linked to "any other enquiries being undertaken by the Major Investigation Team".
More top news
Hundreds of council workers have gathered in sports centres and town halls across the region to count the votes in the 2016 local elections.
The votes are being counted in 22 councils across the Anglia region in the biggest test of political opinion since the General Election.
Clear skies overnight but remaining frost-free. Another sunny day tomorrow and increasingly warm as we head towards the weekend.