A dead woman lay undiscovered in her home for two months before neighbours raised the alarm after seeing thousands of flies in a window of her house.
The body of Brenda Williams, 68, was found on the stairs at her home in Dolgellau, Gwynedd, on 2 September.
The body was in such a decomposed state that pathologists were unable to determine the cause of death, her inquest was told.
The coroner said lack of evidence meant an open verdict was the only option.
Pc Rhys Morgan Jones, who was called out to the house, could not get in and specialist equipment was needed.
The front and back doors were both locked from the inside with the keys remaining in the locks, and there was no evidence anyone else had been inside.
Pc Jones told the inquest the smell was overpowering, with thousands of flies everywhere.
He agreed that because of the position of the body Miss Williams had not fallen down the stairs and had merely sat on the bottom of the stairs.
The inquest heard that Pc Jones searched the house and found food with an expiry date of 8 July and a shop receipt dated 1 July.
Miss Williams' brother Dennis, from Shrewsbury, told the court he had visited his sister on 5 July and she had seemed well, but he had had no contact with her after that day.
Coroner Dewi Pritchard Jones said: "It is a sad reflection on society when an elderly woman's body can lay undetected in her home for two months.
"Everything points to death by natural causes, but there is no pathological evidence of that.
"I am sure that there is no evidence of any trauma or of anyone else being involved."