A man and a woman have been arrested in connection with the human remains found in a Mansfield garden earlier this month.
The two have been held on suspicion of murdering a couple in 1998.
The arrests follow the discovery of human remains buried in the back garden of a house in Blenheim Close, Forest Town in Mansfield, Nottinghamshire on Wednesday 9 October.
Nottinghamshire Police said that while formal identification has yet to be confirmed, officers believe the remains are that of elderly couple William and Patricia Wycherley, who lived at the house in the 1990s and, according to neighbours, disappeared in 1998.
The arrested 57-year-old man and 55-year-old woman remain in police custody in Nottinghamshire for questioning, a force spokeswoman said on Thursday.
A murder inquiry was launched after the bodies were unearthed.
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Officers have said Mrs Wycherley is believed to have been born in Fulham, west London, and would now have been 79.
Nottinghamshire Police said results from bone analysis had shed further light on the remains found at the semi-detached house in Blenheim Close.
One of the bodies is believed by experts to be that of an elderly white man who was older than 60, well-built and around 5ft 8in.
The second set of remains is likely to be that of a well-built white woman, who was 40 or older and around 5ft 6in.
Although the cause of death has yet to be determined in both cases, the female remains have a "distinctive feature in their anatomy".
Detective Chief Inspector Rob Griffin, who is leading the inquiry, previously said the findings support the theory that the remains are those of the Wycherleys.
He said: "Bill and Pat, who would be 100 and 79 respectively if they were to still be alive today, were known to be quite reclusive.
"But with help from relatives and old friends we are starting to build a picture of their lives and, more importantly, their movements in 1998, when neighbours say they simply disappeared."