In March 1989, the South Armagh Brigade of the Irish Republican Army (IRA) carried out a bold, meticulously planned ambush near the border, killing two senior officers of the Royal Ulster Constabulary (RUC). The attack became one of the most high-profile blows against British policing in the North during the final phase of the conflict known colloquially as ‘the Troubles’. “In the years that followed, claims emerged of Gardaí in the South tipping off the IRA – allegedly enabling republicans to prepare and execute the ambush.

The ambush was the culmination of an extended surveillance campaign lasting most of 1988 and 1989 by the IRA’s elite South Armagh unit, whose operations had long frustrated British forces along the heavily militarised border between North and South.

The RUC, whose reputation was shaped by decades of sectarianism a ...