In death, as in life, Captain Robert Nairac was one of the most mysterious and divisive figures in the Troubles. Just an hour before he was abducted and killed by republicans, he was in a South Armagh pub singing 'The Broad Black Brimmer' and other IRA songs.

On 14 May 1977, he was operating undercover in the Three Steps Inn in Drumintee, trying to gather information on the IRA and work his way into republican circles. He was also meeting an informer.

The British army intelligence officer put on a Belfast accent and told customers he was Ardoyne republican Danny McErlaine. Nairac (29) got such applause after his first song, that he sang three more. But not all the 150 customers in the pub fell for his story.

Nairac was challenged as he left the premises just before midnight. A struggle broke out and he was bundled into a car and driven across the border into Co Louth. Another car load of republicans followed. He was beaten, interrogated, and shot dead in Ravensdale forest.

Last week, Kevin Crilly (59) from Jonesborough was charged with Nairac's murder.

Crilly is the seventh person to be charged in connection with Nairac's killing. In December 1977, Liam Townson (24) from south Armagh was convicted of the murder by the Special Criminal Court.

The following year in Belfast, two other south Armagh men were convicted of murder, one of manslaughter, one of kidnapping and one of withholding information. All the men have long been released. Two other men wanted for the murder fled to the US.

Childhood summers

Nairac was born in Mauritius but grew up in England, the son of an eye surgeon. He spent childhood summers with family friends in Dublin and Spiddal, which led to his interest in Ireland.

He read medieval and military history at Oxford where he excelled in sport, especially boxing. He went three rounds with a young Belfast man Martin Meehan, who would become an IRA commander, when Meehan was boxing in England.

A keen falconer, Nairac kept a bird in his room in Oxford which was used in the film Kes. Nairac joined the Grenadier Guards where he gained a reputation for being charming, eccentric, and a romantic loner.

He worked for 14th Intelligence Company, talking regularly about infiltrating the IRA and taking chances many colleagues thought suicidal. He often crossed the border into the Republic, even taking a dog on a fishing trip.

He wasn't an SAS member but had been on one of its training courses. Ex-SAS officer Ken Connor said: "Before his death we had been very concerned at the lack of checks on his activities. No-one seemed to know who his boss was and he appeared to have been allowed to get out of control, deciding what tasks he would do."

One republican said: "He thought he was smart but he was actually a bit of a clown. He fancied himself as Lawrence of Arabia. He reckoned he could put on a fake accent and the stupid Irish would believe him."

Miami Showband massacre

There have been persistent claims Nairac was more sinister and colluded with loyalists. He allegedly had close links with the Mid-Ulster UVF, including with Robin Jackson – the Jackal – implicated in the Dublin and Monaghan bombings.

Ken Livingstone said Nairac was probably involved in the Miami Showband Massacre. Ex-MI6 operative Fred Holroyd claimed Nairac had boasted of his involvement in the 1975 murder of IRA member John Francis Green and shown him a polaroid photograph of Green's corpse taken after the assassination.

Nairac's abduction and murder weren't planned and most of those involved were drunk. In Ravensdale, although brutally beaten, Nairac wouldn't admit his true identity. He tried several times to escape.

When he asked for a priest, one of his abductors posed as a priest in an attempt to elicit information. Nairac's last words were, "Bless me father for I have sinned."

Suspected in several murders

Liam Townson, convicted of the murder, described Nairac as "the bravest man I ever met – he told us nothing". The British posthumously awarded him the George Cross.

Bloodstains, teeth and hair were later discovered at the scene but Nairac's body was never found. Rumours that it had been horrifically disposed of at a local meat processing factory are untrue. It is believed he is buried in farmland. The IRA claim the grave cannot be located.

Despite the brutality of his killing, there remains little sympathy for Nairac in south Armagh. Ex-Sinn Féin representative Jim McAllister says: "Those who hope the bodies of the other Disappeared, like Gerard Evans and Charlie Armstrong, are found, don't care about Nairac.

"He wasn't an ordinary young soldier, deserving compassion, who found himself in unfortunate circumstances. He was a member of the British intelligence services suspected of involvement in several murders himself."