Alasdair Cooke said it is important people do not forget the Tullyvallen massacre, where IRA men shot dead five Orange Order members close to Newtownhamilton in south Armagh on the night of September 1, 1975.
Gunmen burst into the isolated Tullyvallen Orange Hall during a meeting of Tullyvallen Guiding Star Temperance LOL 630 and opened fire, murdering John Johnston, 80, 73-year-old James McKee and his son Ronnie McKee, 40, Nevin McConnell, 48, and William Herron, 68, who died two days later.
Six other men were injured in the attack.
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A 2lb bomb was also left outside the hall. It was defused by the Army.
A memorial plaque in the hall remembers the five victims as well as fellow lodge members William Meaklim, who was murdered two weeks before the attack, and Joseph McCullough,