Nottinghamshire Police have launched a murder inquiry into the deaths of William and his wife Patricia Wycherley, after their remains were found in the back of a garden.
Police named the victims as Mr Wycherley, who would now be 100, and his wife Patricia, 79.
Their bodies were uncovered by officers who were led to the semi-detached house in Mansfield last week after a tip-off.
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The couple moved in to the two-bedroom property at 2 Blenheim Close, Forest Town, in 1987, but vanished after 1998.
Post-mortem tests have been carried out on the bodies but have so far proved inconclusive.
Speaking at a press briefing in Nottingham today, Detective Chief Inspector Rob Griffin said: "Whilst it's difficult to ascertain cause of death given the passage of time, the circumstances in which the skeletal remains have been found is suspicious and we have now launched a murder inquiry."
He added: "Insofar as suspects are concerned we are entirely open-minded but it's far too early in the investigation to be talking about suspects at this stage.
"The focus of the investigation is on the Wycherleys themselves and the goings on at 2 Blenheim Close back in the 1990s."
Mr Griffin said there was no known motive for the murders as yet.
Mr Griffin said a "key part" of the inquiry is who lived at the address between 2000 and 2005.
Asked whether he knew who lived there during that period, the officer said: "What happened around that period we're really interested in but at this moment in time, no, we don't know".
He said neighbours past and present had described the couple, who are believed to have had a daughter, as "reclusive" and said they had kept to themselves.
They have never been reported missing and police have so far been unable to find any trace of them either alive or dead since the late 1990s.
Mr Griffin said: "At this time we are unable to categorically say that the remains that have been uncovered are those of the Wycherleys but I am confident that the two sets of skeletal remains are indeed those of Patricia and William."
Appealing for information, he said: "I would like anybody who knows or knew Patricia and William, or Bill, as he was known - in fact, sometimes known as Geoff, as that was his middle name - back in the 1990s to come forward today."
He added: "I would also be keen to talk to anybody who lived in the area of Blenheim Close anytime between 1990 and 2005. If they can tell us anything about the address of 2 Blenheim Close, its occupants, its visitors or anything that took place there".