The husband and wife, named locally as Barry and Kath Haberfield, were discovered in their home at Claerwen Close, in Aberdare, south Wales, on Tuesday.
Police have been treating the deaths as “unexplained” and were hoping that post-mortem examinations being carried out yesterday would offer an indication as to what killed them.
But the results were ‘inconclusive” and further tests must now be carried out on the couple.
Neighbours Ken and Marlene Davies said the deaths had shocked the local community.
The couple are understood to have lived in the close for nearly 30 years.
Mrs Davies, 73, said: “We only saw them two days before Christmas Eve and they seemed fine.
“Kath had been ill with a respiratory problem, but she had been going to see the doctor and appeared to be managing OK.
“They were both lovely people and very good neighbours. It is strange to think we will not ever see them again.
“It’s such a shock and it truly is awful news that has rocked everyone here.”
It is understood that retired supermarket manager Mr Haberfield, 71, and his former shop worker wife, 58, who used to work for Marks and Spencer, were found dead after two neighbours called round to check if they were all right after seeing a light on downstairs in the morning.
South Wales Fire Service confirmed its firefighters were called to the couple’s bungalow on Tuesday morning to check for carbon monoxide.
A spokeswoman said: “Fire crews arrived at the scene at around 9.25am before leaving at around 10.35am.
“During that time they did not detect any carbon monoxide.”
Police said they did not know what caused the couple’s deaths and further tests were needed, which could take up to six weeks.
The couple’s next of kin have been informed.
Another neighbour, Dilys Evans, said: “They were lovely people – both of them had been unwell but we just don’t know what has happened.
“They lived there alone but were very much part of the strong community we have here.”