Collusion by British state forces in killings perpetrated by loyalist paramilitaries was a dubious hallmark of the 'dirty war' in the north of Ireland. Now, more than twenty years since the Good Friday Agreement, the story of collusion remains one of the most enduring and contentious legacies of the conflict, a shadow that trails British counterinsurgency to this day. Here Mark McGovern turns back the clock to the late 1980s and early '90s - the 'endgame'...