In 1972, 13 Catholic demonstrators in Northern Ireland were killed when British soldiers opened fire on a group of protesters. It became one of the most significant and bitter events in the Troubles in Northern Ireland (as well as the basis of a U2 song). In June, after a 12-year investigation confirmed indisputably that the protesters were unarmed, David Cameron offered a public apology in the British House of Commons. After noting that "you do not defend the British army by defending the indefensible," Cameron went on to say, "What happened on Bloody Sunday was both unjustified and unjustifiable."