This documentary-style drama attempts to shed light on the notorious events of Jan. 30, 1972. In the Northern Irish town of Derry, a protest march led by Ivan Cooper was fired upon by British troops, killing 13 protesters and wounding 14 more. The event became a tragic touchstone in the Irish independence movement. Dark, forceful and admirably unburdened by the sheen of Hollywood filmmaking, this gritty chronicle is pure gut-punch cinema. 107 minutes R.