The British Army officer who was the initial source of the garda collusion claims being examined by the Smithwick Tribunal into the IRA murders of two senior RUC officers was killed in Afghanistan two years ago.
Lieutenant Colonel Rupert Thorneloe was killed by a landmine in Helmand Province in July 2009.
In 1991, Lt Col Thorneloe was the British Army's intelligence liaison officer with the RUC in south Armagh.
He took a particular interest in the killings of Chief Supt Harry Breen and Supt Bob Buchanan in March 1989.
He later spoke to the journalist and author Toby Harnden, who wrote an account of the killings with the first mention of possible collusion by a member of An Garda Siochana in his 1999 book, Bandit Country, about the IRA in south Armagh.
This account, and subsequent other reports in newspapers, prompted the calls for the inquiry into the deaths -- which were seen by unionists as counterbalancing the Bloody Sunday and other inquiries demanded by republicans.
There was an inconclusive report by Canadian judge Peter Corry into the two RUC officers' deaths and this has been followed by the inquiry by Judge Peter Smithwick, which began its work in 2005 and is now at the public-inquiry stage.
In Bandit Country, Harnden, then Ireland correspondent for the Daily Telegraph, wrote that Breen had told a colleague that he was uneasy before the trip to Dundalk garda station and "that he was concerned about one garda officer ... whom the RUC Special Branch believed might be working for the IRA."
Although he has not and will not disclose his sources, Harnden became friends with Lt Col Thorneloe and they became friends. He visited him and his regiment in Afghanistan in 2009.
He subsequently wrote a book on the Welsh Guards in Helmand and about Thorneloe's death.
In Dead Men Rising, Harnden said he first met the officer while Thorneloe was serving as an intelligence officer in south Armagh and that he helped with his book about the IRA.
He confirmed to the Sunday Independent that Thorneloe was one of the sources of his claims about garda collusion. However, the reporter, who is now based in Washington as the Telegraph's US correspondent, said he expected to be called to give evidence at the tribunal and so could make no further comment.
Lt Col Thorneloe was widely regarded a rising star and likely one day to lead the British Army. He had been awarded the OBE for his services in Iraq.
He led his regiment to Afghanistan in April 2009.
After carrying out minesweeping alongside his men, he had just returned to his armoured personnel carrier when a large mine exploded underneath it killing him and Trooper Josh Hammon, 18, instantly and injuring three others.