McGurk's Bar bombing tombstone and commemorative plaque

On 4 December 1971, the Ulster Volunteer Force, an Ulster loyalist paramilitary group, detonated a bomb at McGurk's Bar in Belfast, Northern Ireland, frequented by Irish Catholics–nationalists. The explosion caused the building to collapse, killing fifteen Catholic civilians—including two children—and wounding seventeen more. It was the deadliest attack in Belfast during the Troubles.

Despite evidence to the contrary, the British security forces asserted that a bomb had exploded prematurely while being handled by Irish Republican Army members inside the pub, implying that the victims themselves were partly to blame. A report later found that the Royal Ulster Constabulary, the police force in Northern Ireland at the time, were biased in favour of this view and that this hindered their investigation.

Source: Wikipedia