Former senator Mr George Mitchell still wonders whether what he calls a "despicable" attempt to smear one of his aides might have been a British "dirty trick".
In his new book, Making Peace, which has been published in the US, Mr Mitchell recalls the storm over media allegations that his senior aide, Ms Martha Pope, was having an affair with a Sinn Fein member and former IRA convicted bomber, Mr Gerry Kelly.
Ms Pope successfully sued several newspapers for damages and obtained a retraction of the allegations which were said to be based on secret MI5 intelligence reports. However, Mr Mitchell writes that at the time, December 1996, he and Ms Pope were "puzzled by the response of the British government". The NIO, "instead of directly denying the allegations . . . simply referred to my denial".
Mr Mitchell had called the allegations "scurrilous" and "absolutely and totally false". When he spoke to the then Northern Secretary, Sir Patrick Mayhew, "he told me that they [the British government] didn't think there was anything to it, and that they didn't comment on matters of intelligence.
"He couldn't even confirm the existence of a report, let alone let me see it. It was a very unsatisfying situation."
Yet, several days later, Mr John Steele, the director of policing and security at the NIO who was travelling in the US, told the media: "I read all the intelligence in Northern Ireland . . . I never saw anything to support even an allegation."
Mr Mitchell in his book asks: "Why had not some British official made a statement like that on Sunday when the story broke, or even on Monday?" He writes: "Did Steele inadvertently [or intentionally] violate NIO policy when he made his comment?"
(Making Peace is published in the US by Alfred Knopf)