New information regarding the kidnapping of champion racehorse Shergar is brought to light in a Channel 4 documentary to be screened on Thursday.

Shergar was kidnapped on the evening of the 9 February 1983, from the Ballymany Stud in County Kildare, never to be seen again. Although his kidnappers have never been officially identified, most evidence points to the involvement of the IRA.

Nicknamed ‘Shergar the Wonder Horse’, he most famously romped home to victory in the 1981 Derby, winning by a 10-length-margin. This was followed by wins in the Irish Derby, the King George VI and the Queen Elizabeth Diamond Stakes. He was named European Horse of the Year in 1981.

The stallion became a racing hero in Ireland, where he was born and trained. He was retired to stud at the height of his racing success. His owner, the Aga Khan, sold 34 shares in the horse, which were valued at £8.5 million.

This was a crucial factor overlooked by the kidnappers, the documentary claims. Forty shareholders were not prepared to fork out even £1,000 each for the safe return of the racehorse, concerned that if they had done so, they would have condoned the kidnapping as a successful means of extortion.

The Channel 4 programme not only investigates the shambolic nature of the kidnapping itself but also the chaos that surrounded the hunt for Shergar. It was not until eight hours after the event did anyone think to contact the Gardai (Irish police force), and the subsequent search appear to be a series of police bungles.

An IRA informant is one of the interviewees on the program. Sean O’Callaghan reveals that, as has been previously suggested, the horse was probably shot within hours of being snatched. With little knowledge of horses, the gang were unable to cope with a lively stallion at close quarters.

Speculation that a skull found in County Kerry in 2000 belonged to Shergar was quickly dismissed, as tests established that the skull belonged to a horse much younger than the racing legend when he was abducted.

The film combines new interviews with extensive film reconstruction. Beginning with the whirlwind career that made Shergar a household name, the documentary follows the sequence of events that led to his kidnapping and the decades-long police investigation.

· Who Kidnapped Shergar? Thursday 18 March, 9pm Channel 4.