Denis Martin Donaldson (1950 – 4 April 2006) was a volunteer in the Provisional Irish Republican Army (IRA) and a member of Sinn Féin who was murdered following his exposure in December 2005 as an informer in the employ of MI5 and the Special Branch of the Police Service of Northern Ireland (formerly the Royal Ulster Constabulary). It was initially believed that the Provisional IRA were responsible for his killing although the Real IRA claimed responsibility for his murder almost three years later. Wikipedia
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