The British government refused to pass on what it knew about the fate of German industrialist Thomas Niedermayer to his family because it might lead to "awkward" media attention, according to released cabinet papers.
Mr Niedermeyer, who was manager of the Grundig electronic factory and German consul, was abducted from his home in Belfast on 27 December 1973, but no group admitted responsibility.
Years later, it was revealed that the British government was in talks with the IRA who had kidnapped him and wanted the release of Marian and Dolours Price from prison in England.
These talks came to a halt when Mr Niedermayer was accidentally killed by the kidnap gang.
At the time, the British government denied that any ransom demand had been made and the IRA denied being involved.
Mr Niedermayer's body was not found for nearly seven years.
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After the kidnapping, Mr Niedermayer's wife Indeborg stayed in Belfast with their two teenage daughters Renate, 15, and Gabriella, 18, hoping to hear news of her husband.
It was the height of the Troubles and wild rumours were circulating about what happened to Mr Niedermayer, including that the kidnap was the result of an affair or business dealings.
Mrs Niedermayer wrote to then British Prime Minister Harold Wilson in March 1974 asking him as a "husband and a father" to give her more information after three months of police investigation "proved fruitless".
"I sincerely believe now that your government in conjunction with the German government seem to know more about this kidnapping than you are prepared or allowed to admit in public."
The cabinet files contain a draft reply from the prime minister, which offered sympathy, but stated "there is still no evidence on what has happened".
The files reveal that the German government kept asking for more information, including a request made in person to the then Foreign Secretary James Callaghan by his German counterpart, after an article appeared in a newspaper in June 1974 stating that "four of the five terrorists" involved in the kidnapping were in prison for other offences.
The British Foreign Office and other departments agreed a line to be given to the Germans "which encapsulate very nearly the whole truth of what little we know", according to GW Harding of the Republic of Ireland Department of the Foreign Office.
Mr Harding wrote to the British Ambassador in Germany on 2 August, 1974 in a letter marked 'secret' that the hypothesis being shared with the Germans was that Mr Niedermayer’s kidnapping was a private venture by a small independent IRA group who intended to take him to the Republic and hold him hostage there.
The story about suspects being in custody was dismissed as "gossip".
The line was given to a German diplomat during a meeting in the Foreign Office on 2 August and he was told that the British government did not know whether Mr Niedermayer was picked because of his prominent position as German consul and manager of the factory, or whether his private life was involved.
It seemed probable that he died soon after he was kidnapped, possibly from natural causes.
The Grundig company would pay "any sum" for Mr Niedemayer's release
The German diplomat asked if they could pass on this information to Mrs Niedermayer, but Mr Harding said he told them that if she was told she might leak it to the press, which in turn would lead to another wave of public interest "which the Germans would find as awkward as we would", stated Mr Harding.
Later that year, the Germans were again in contact after a newspaper story reported on 16 December, 1974 that "special intelligence services" had employed "dirty tricks" to cover up a rejection of a ransom demand.
In a memo, Mr Harding said he told the Germans this allegation was "totally unfounded".
The files also reveal that in the immediate aftermath of Mr Niedermayer's abduction, the German government pressed the British to allow a ransom to be paid.
In a face-to-face meeting in London the day after the kidnapping, the German ambassador Karl-Guntgher von Hasse told Northern Ireland secretary Francis Pym, that the Grundig company would pay "any sum" for Mr Niedermayer’s release.
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According to notes taken by British civil servants, Mr Pym replied that if a ransom was paid to the IRA then it would increase their ability to kill British soldiers and any demand for the exchange of prisoners would raise "terribly serious problems".
The German ambassador said the abduction of Mr Niedermayer could lead to loss of investment and asked how would the British government balance that loss against the strengthening of the IRA’s position.
The Northern Ireland secretary replied that they were separate considerations and that the British government would not weigh one against the other.
Germany had an ambassador murdered in Guatemala three years earlier after that government refused to negotiate.
The ambassador said German public opinion had to be taken into account while the Northern Ireland Secretary replied that British public opinion also had to be taken into account.
The German ambassador said his government applied the "yardstick of humanity" and that their efforts were concentrated on helping those directly involved. However, the Northern Ireland Secretary insisted that to bargain with the IRA was a very serious problem for the British government.
Two files from the period 1973 to 1974 are still being withheld.
Mr Niedermayer's body was found buried underneath an illegal rubbish dump in 1980 not far from his home after the RUC received information. A medical examination found he had been pistol whipped and it was reported that he died during an escape attempt. His body was bound and gagged and buried face down.
Two men were later convicted and sentenced to five and 25 years imprisonment for their involvement.
There was thought to have been an element of a private grudge as the IRA man believed to have organised the kidnapping was Brian Keenan who had worked as a shop steward in Grundig and had been involved in confrontations with Mr Niedermayer.
His wife left Northern Ireland, but returned to Dublin to take her own life in 1990. Within four years both her daughters had also died by suicide, followed by her son-in-law in 1999.
