With their frank descriptions of homosexual exploits and carefully noted payments to rent boys, the papers were just what British intelligence needed to disgrace the Irish nationalist Sir Roger Casement and send him to the gallows.
Ever since they were circulated to prominent politicians and writers early in 1916, Casement's so-called "Black Diaries" have been the subject of claim and counter-claim over whether the five volumes were genuine or forged by MI5.
Yesterday, a group of Anglo-Irish academics attempted to lay the debate to rest by revealing the results of more than a year of forensic tests which they insisted prove "inescapably and conclusively" that the diaries were written by the revolutionary himself.
Such has been the power of the controversy to inflame passions on either side of the Irish Sea that the £15,000 study was carried out with the personal backing of Tony Blair and his Irish counterpart Bertie Ahern.
Casement, an Ulster Protestant and former British diplomat who exposed the brutality of the slavery in the Congo before joining the nationalist Irish Volunteers in 1912, was arrested at the height of the First World War in 1916.
He had landed in County Kerry to support the Easter Rising from a German submarine, accompanied by a shipment of 20,000 rifles, after striking a bargain with the German high command. Berlin pulled out of an agreement to send troops at the last minute.
Following his conviction for treason in London, extracts from the diaries were sent to senior figures in the British establishment, ranging from the Archbishop of Canterbury to Sir Arthur Conan Doyle, creator of Sherlock Holmes.
The lurid references to homosexual sex, including observations on the size of his lovers' genitals, saw pleas for clemency diminish to almost nothing. Casement was hanged at Pentonville Prison in London on 3 August 1916.
A working group headed by Goldsmiths College, London University, compared Casement's musings with other documents known to have been written by him. Analysis of the ink used and variation in the pen stroke and handwriting characteristics, using microscopes and video cameras, proved that only Casement could have written the diaries, a press conference was told. The outlines of the letters and the pressure applied to pages matched identically pages from other documents.Reuse content