Stefan, 25, had been missing for 11 days when his body was found on the high-water mark on the beach at Occumster, MAP close to where he lived.

His body had suffered considerable damage from marine life, so clearly had been at sea for some days.

As well as a broken skull and broken leg, his front teeth had been knocked out and the joints of his fingers had been pulled apart, suggesting a brutal beating.

 Occumster Bay, where Stefan’s body was found

Police and Stefan’s family heard from locals that Stefan, who had seven siblings, was seen going into a house on the night he disappeared.

It was also claimed he had been murdered and his body hidden in a luxury caravan for three days, before being dumped at sea.

But Police Scotland quickly concluded there had been no foul play, insisting that Stefan either fell more than 100 feet from the cliffs in the dark, or was suicidal and jumped.

The theory fails to explain how his body reached the water, later to wash up at the high-water mark, some 75 feet from the foot of the cliffs.

It took more than four months for his family to persuade police to search the house where they feared he had been murdered, and a bloodstain matching Stefan’s DNA was found.

Bedding locals said had been dumped from the caravan at the centre of the mystery was collected by police, but over a period of months, amid repeated questioning by the Sutherland family, it emerged that it had never been forensically tested, and has now been destroyed.

The family has also been told by police that the caravan has been sold more than once since September 2013, and that they cannot trace it now.

Police Scotland and the Crown Office maintain there are no suspicious circumstances surrounding the death, and that no evidence has emerged that warrants taking action against anyone.

The Crown Office is considering the possibility of a Fatal Accident Inquiry into the circumstances surrounding Stefan’s death.

But his family intends to press for a new and comprehensive police investigation, hoping someone might yet face a charge for murder.

Stefan’s mother, Sandra, said: “For over two years now I have been haunted by how my son might have died and how he sustained the horrific injuries that prevented us from identifying his body. It is hard to adjust to the fact that we will never see Stefan again. He was so alive, energetic, enthusiastic. Now we just have memories.”

The family believes most police action that has followed, mainly in response to their prompting, has been about justifying the early decision not to pursue it as a murder case, rather than delivering justice.

His father, Sandy, said: “When we’ve argued against the suicide theory because we know his state of mind better than the police, they’ve gradually moved over to the accident theory. But he would never have walked over the cliffs in the dark. He knew better. Also, far from being a short-cut home, a walk that way would have taken him away from home.”

Stefan’s brother George added: “The whole situation has devastated the family. You have to lose a close family member to know how it affects you. Our situation was made much worse when liaison officers informed us that 98% of people interviewed in a door-to-door enquiry mentioned a name, yet detectives say there are no suspicious circumstances.”

Yesterday, a Police Scotland spokesman said: “Police Scotland can confirm following a thorough investigation into the death of Stefan Sutherland in September 2013, there were no suspicious circumstances and as with all sudden deaths a report was sent to the Procurator Fiscal.”

A spokesman for the Crown Office said: “Comprehensive and thorough investigations have been carried out into the death of Stefan Sutherland and no suspicious circumstances have been discovered.”

At the moment, the Sutherlands are not interested in an FAI.

Mr Sutherland said: “There is abundant evidence that our son was murdered. He did not pull his own fingers apart at the joints or knock his own teeth out. He did not fall or jump from the cliffs and then walk into the sea. It is clearly a matter for a criminal court, not an FAI.”