The appalling brutality of the attack has sent shock waves even among those who have lived through the 3,500 killings of the Troubles. It has also increased the dread that this summer's marching season could be as disastrous as last year - for the death had its roots in the bitter business of contested parades.
The officer who died was Gregory Taylor, a 41-year-old constable who lived two miles outside Ballymoney in County Antrim. He was the father of three children, one of whom suffers from cerebral palsy.
He had gone for a drink with two friends, one of them another off-duty policeman, to Kelly's Bar in Ballymoney, a small pub crowded that night with more than 100 customers.
In the upstairs lounge he was identified as a policeman, jostled and abused about the RUC's action in keeping a recent Orange parade out of the Catholic village of Dunloy. Someone shouted at him: "Why don't you clear off and do your drinking in Dunloy?" A number of those in the bar were members of local loyalist bands.
Aware that he was in danger, the constable used his mobile phone in an attempt to summon police help. The fact that it was not forthcoming is now the subject of an internal RUC inquiry since it has emerged the nearest patrol car was several miles away.
When the two constables left the bar, in the early hours of Sunday, a reception committee was waiting in the street. The other policeman claimed he was a doctor and was chased away, but Constable Taylor was attacked mercilessly. As he lay bleeding in the gutter, his assailants took turns to kick him and stamp on his head. The constable did not take long to die; but when someone suggested getting help, one of the mob yelled: "He doesn't need a doctor."
Last night,15 people, including a number of loyalist bandsmen and three women, were being questioned by police about this latest gruesome addition to the seemingly endless list of victims of the Troubles.
Ballymoney has escaped much of the effect of the Troubles, but over the last year some of the surrounding parts of County Antrim have been affected by disturbances arising out of last year's marching season. Residents of Dunloy objected to loyalist parades and in the ensuing stand-offs the RUC prevented the marchers from going through.
In nearby Ballymena, political heartland of the Rev Ian Paisley, loyalists retaliated by staging weekly pickets of Catholic churchgoers. These protests dragged on through the winter, and as a result the marching season - traditionally a feature of the summer - in effect turned into a year-round phenomenon.
On most weekends the protests passed off reasonably peacefully, but on occasion crowds of loyalists clashed with the sizeable force of RUC assigned to ensure safe passage for the churchgoers. In nocturnal follow-ups, the homes of several RUC officers were attacked. And on Saturday night, the loyalists' smouldering anger ignited with murderous results.