How the Suzanne Pilley murder investigation progressed

But while the mystery of Ms Pilley’s last resting place remains unsolved, detectives were not hunting for an unknown killer with no obvious links to the victim.

Detective Superintendent Gary Flannigan, pictured, said it was a “ground-breaking” case for Lothian and Borders Police due to its complexity, with the combination of a missing body and the volume of witnesses and CCTV to be scrutinised.

But he said the force’s handling of the disappearance of Louise Tiffney, 43, from her Dean Village home on May 27, 2002 would prove vital experience. Despite repeated searches, including digging in the 60,000-acre grounds of Gosford House in East Lothian, the mother-of-two’s body has never been found.

While her 18-year-old son Sean was cleared of murder on a not proven verdict in 2005, Det Supt Flannigan said the probe yielded many lessons.

From an early stage, investigators worked closely with prosecutors to build what was ultimately an entirely circumstantial case against Gilroy. Many convictions are secured in Scotland’s courts through forensic evidence, but here only specialist “cadaver” dogs trained to trace the scent of human remains or blood would provide such a link. Officers would have to rely on old-fashioned police work, spending tens of thousands of hours following up every lead, interviewing hundreds of potential witnesses, and trawling CCTV footage.

Det Supt Flannigan said that the discovery of the make-up on Gilroy’s hands to hide what he said were gardening injuries was a turning point in the case.

Detective Constable Colin Fordyce, a keen gardener himself, could find no sign of the alleged work in the cramped garden of Gilroy’s home.

At a briefing later that day, Gilroy’s status was changed from witness to “suspect”.

The specialist dogs were brought in from South Yorkshire Police and showed interest in areas in both the basement of the IML offices and the boot of Gilroy’s Vauxhall Vectra.

From that point the net began to close on Gilroy.