Who kidnapped the Derby-winner Shergar and why?

It is one of the great unsolved mysteries - what happened to Shergar?

The bookends of the thoroughbred's life are well-known.

He was born in Kildare in 1978 and kidnapped by an armed gang in 1983.

It was believed Shergar - valued at £10m - was taken by the IRA, which was short of money and looking for new sources of funding.

He was expected to be a source of profit for the syndicate which owned him.

The kidnapping overshadowed Shergar's career - but many in the racing fraternity still speak with awe at the ease with which he could win.

Cliff Lines, Shergar's work jockey, said: "As a two-year-old I sat on him.

"He just gave you that special feel and after that little bit of work, the boss came walking up and I just said to him: 'I think this is the one you've been waiting for.'

"And Shergar just went from strength to strength."

Shergar soon won both the Epsom Derby and the Irish Derby.

The horse's owner, the Aga Khan, then decided to retire him to stud, and Shergar returned to Ireland in a blizzard of headlines.

He attracted crowds wherever he went.

Former IRA intelligence chief Kieran Conway said Shergar also attracted the attention of the terrorists.

He said stealing the horse was a good idea as the Aga Khan had no political issues regarding paying any ransom.

"There was just a shortage of cash, bank robberies and the like were more difficult than they had been in the early 1970s - they had to get it somewhere so they turned to kidnapping," he told the BBC.

Jim Fitzgerald, who was head groom at Ballymany Stud, remembers clearly what happened on the night of 8 February 1983.

"These gangsters came in with guns," he said.

"They said what they were there for, so they brought me down to the stable where the horse was and I put him in the small horse box for them gangsters to take him away."

Mr Fitzgerald was also taken away by the gang and eventually released.

Little evidence was found at the scene and the trail quickly went cold. Calls to the Aga Khan's office and to the Ballymany Stud led nowhere.

The kidnap gang was never heard of again.

No ransom was ever paid.

No-one ever officially admitted responsibility and no-one has been convicted of a crime related to Shergar - the case remains open.

However, during attempts to prove Shergar was dead to get insurers to pay out, an account of what happened was given by jailed IRA informant Sean O'Callaghan.

David Cosgrove, who helped shareholders in their attempts to recover an insurance payout, said O'Callaghan claimed the horse was killed within 24 hours.

"O'Callaghan was absolutely definitive that the animal had died very quickly.

"The animal was taken in a horse box on the road up to Leitrim, he had become excitable - they stopped several times to quiet the horse and they discovered he had fractured one of his leg bones.

"He was in considerable distress and not having any veterinary back up they felt they had no alternative but to destroy the horse and that is when they shot him."

O'Callaghan said Shergar's remains were left in the countryside around the village of Ballinamore, near the border.

Film maker Alison Millar, who made the Shergar documentary, believes people there know the location - but when she visited the area no one was prepared to discuss it.

Clare Balding, whose father's horse raced against Shergar, said: "He is like a ghost figure. He was here, he was stunning and then he disappeared."

Searching for Shergar is on BBC One NI on Thursday 7 June at 21:00.