What is not disputed is that Captain Nairac was kidnapped by the IRA after spending the evening of May 14, 1977, undercover at a Republican bar just inside the Northern Irish border.
He was then bundled into a vehicle in the pub’s car park just before midnight and taken into the remote Republic of Ireland countryside where he was tortured and eventually killed the following day.
While his pistol and traces of his hair and blood were later found to support the events so far, the 28-year-old Grenadier Guardsman’s remains have still to be recovered.
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Now comes the guesswork.
Why was the Sunderland-raised soldier in the pub on his own in the first place?
Was he meeting a contact so that he could feed military intelligence back to the British services at the height of the Ulster Troubles?
Was he – as the IRA claimed – a member of the feared SAS regiment and therefore a notable scalp in the terrorist organisation’s battle for a united Ireland?
Did he also work with Loyalist or Protestant paramilitaries to orchestrate atrocities against Catholics in the supposed name of keeping Ulster part of the UK?
Or did he become a convenient scapegoat for the British authorities after his death so that other agents could operate without suspicion?
If that is so then was he merely a loose cannon acting outside his limited authority in posing as a native and singing pro-Republican songs just minutes before displaying his boxing prowess as his kidnappers struggled to overpower him?
And what of the theory that his remains were quickly fed to a farm's industrial mincer to remove all trace of his body?
Here, as the 45th anniversary of his execution approaches, we look back at his life, death and search for his body.
August 31, 1948: Robert Nairac is born on the island of Mauritius, in the Indian Ocean, to an English mother and a French-Mauritian father.
1949: Nairac’s parents and their four children move to Sunderland, living in Thornhill Gardens, off Tunstall Road, Ashbrooke, for around 20 years with Mr Nairac working as an eye surgeon at nearby Sunderland Eye Infirmary.
1959: Enrols at Roman Catholic public school Ampleforth College, on the North Yorkshire Moors.
1967: Attends Lincoln College, Oxford University, where he reads medieval and military history. Also excels at boxing and rugby and becomes a keen falconer.
1971: Enters the Royal Military Academy at Sandhurst before joining the Grenadier Guards. Eventually joins his regiment after post-graduate studies at the University College of Dublin.
1973: His first tour of duty in Northern Ireland with the Second Battalion of the Grenadier Guards. Duties were mainly to find paramilitaries and weapons.
1974-75: Joins military intelligence and acts as liaison officer between the British Army and the Royal Ulster Constabulary (RUC).
May 14, 1977: After increasingly undertaking undercover activities, the now Captain Nairac visits the staunchly Catholic Three Steps pub, in Dromintee, South Armagh, where he reputedly sings Republican songs before he is abducted by IRA members, taken across the border and shot dead the following day.
November 1977: IRA member Liam Townson, 24, is convicted of Captain Nairac’s murder after beginning his initial police statement by saying: “I shot the British captain. He never told us anything. He was a great soldier.”
1979: Captain Nairac is posthumously awarded the George Cross for his bravery.
1999: The Independent Commission for the Location of Victims’ Remains (ICLVR) is set up jointly by the United Kingdom and Irish governments to find the remains of 16 “Disappeared” victims of the Troubles.
2011: The last criminal case against Captain Nairac suspects to date ends with the acquittal of IRA member Kevin Crilly, 57, of murder,
As of now, three men, including Townson, have served sentences for murder, another was convicted of manslaughter and two more found guilty of kidnapping and withholding information.
None revealed what happened to his body.
2017: Human remains found in northern France are confirmed as those of teacher Seamus Ruddy, who was murdered by the INLA Republican splinter group in 1985.
The discovery means that Captain Nairac is one of only three of the original 16 Disappeared still to be discovered.
May 2017: The 40th anniversary of his murder sparks fresh pleas to recover his body. Lead investigator Geoff Knupfer labels rumours his remains were fed to an industrial mincer as a “distraction”, adding: “We believe he is buried somewhere in north County Louth.” He also discounts rumours that Captain Nairac was in the SAS and insists military records show he was outside Ulster when Loyalist atrocities were committed.
2019: A search of part of Ravensdale Forest finds no evidence of a grave. A £20,000 Crimestoppers reward is pledged anonymously for information leading to his body’s recovery.
2021: Seamus Maguire, who disappeared from his home near Lurgan, County Armagh, in 1973-74, is added to the list of unsolved Disappeared cases.