The man found dead at a house in Derry has been named locally as Noel O’Sullivan.
A man in his 50s was arrested after the sudden death of the elderly male in Londonderry.
Police confirmed on Wednesday evening that the man, aged in his 80s, had passed away.
The incident happened in the Culmore Road, which would be regarded as an affluent area of the city.
Forensics remained at the scene on Thursday.
Officers stood guard at the front gate and an overgrown garden was visible beyond them.
The dead body lay for a number of days before the alarm was raised with emergency services to call out to the property.
Police attended the house at the end of April when it’s understood they had to force entry as there were concerns about the man’s health.
Watch: Police attend sudden death in Derry
The man was taken to hospital and subsequently discharged.
Carers, accompanied by the police, are believed to have carried out an assessment at his home.
A local source expressed concerns about “cracks in the system that this family have fallen through”.
This afternoon the PSNI said: “Police are continuing to investigate the circumstances surrounding the death of a man, aged in his 80s, in Derry/Londonderry.
“The man’s body was discovered on Wednesday afternoon, 17 July, in a house in the Culmore Road area of the city.
“A man, aged in his 50s, has been arrested in connection with the investigation and remains in custody at this time, assisting with enquiries.
“A post-mortem examination is expected to be carried out on Friday 19 July to determine the cause of death.
“There are no further details at present.”
Local SDLP councillor Catherine McDaid said the community are “in shock” following the incident and passed her condolences to the man’s family.
“It’s absolutely terrible, it’s devastating, the whole community is in shock and our thoughts go out to the family of the man,” she said.
Sinn Féin councillor Sandra Duffy also offered her condolences.
“The local community is shock and saddened to learn of the sudden death of a man on the Culmore Road. My immediate thoughts are with this man’s family and friends at this very sad and difficult time,” she said.
The police are still at the scene and an investigation is ongoing.