Susan and Christopher Edwards, 55 and 57, were to make their first court appearance Saturday, The Guardian reported. Police said the couple were arrested at St. Pancras International Train Station in London.
Susan's parents, William and Patricia Wycherly, who lived in Mansfield near Nottingham, vanished in 1998. Two skeletons were found in October buried in the back garden of their semi-detached house.
Detective Chief Inspector Rob Griffin, who is heading the investigation, said the identities of the remains had not been confirmed. But he said they were almost certainly the long-missing couple, given their physical characteristics and the place they were buried.
Both had been shot.
"Bill and Pat, who would be 100 and 79 respectively if they were to still be alive today, were known to be quite reclusive," Griffin said. "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 neighbors say they simply disappeared."