Very late, I know, but I've finally got round to checking my copy of 'Lost Lives' and found that Wolfgang's informed guess above was not entirely successful. Here is what I found:

[1999:] 896. July 9, 1973: Isaac Scott, Armagh. Civilian, Protestant, 41, single.
A former member of the UDR, he was shot by the IRA at Belleek near Newtownhamilton as he started his car after leaving Tully's, the village pub. Another man was seriously injured in the shooting. The gun attack happened just after midnight, Isaac Scott and a woman having just got into his car when shots were fired through the windscreen, killing him instantly. It emerged sometime after his death that Isaac Scott, who came from Mayobridge, was a former member of 3 UDR in Co. Down. His woman companion told the inquest she did not know if anyone in the bar knew he had been in the UDR or that he was a Protestant. The following month a Catholic man, Charles J. McDonnell, was shot dead nearby in an apparent reprisal. (Lost Lives 377)

924. August 22, 1973: Charles J. McDonnell, Down. Civilian, Catholic, 20, single.
From Carrowmannon, Belleek, he was shot in the head and chest after being abducted by armed and masked UDA/UFF men from outside his fiancée's home. The couple were sitting in a car when the gang ordered him out, drove him a short distance away then shot him 11 times from close range. As the gunmen took him away they told his fiancée, 'This is for Isaac Scott.' The shooting took place not far from the Mayobridge home of Isaac Scott, who had been shot dead the previous month. Charles McDonnell's 18-year-old fiancée gave evidence at the inquest. She said: 'We went to bingo and had just got home at 11.30 p.m. We were sitting talking about the wedding next year when a car drew up behind us. We didn't take any notice of it because I thought it was my brother coming home. Suddenly the door burst open and the gunmen, wearing masks, ordered Charles out. They told me to go inside and the last I saw of Charles was when they bundled him into the back seat of the car. He didn't do anybody any harm - what am I going to do without him?' A man calling himself 'Captain Black of the UFF' called a Belfast newspaper and accepted responsibility for the McDonnell murder. A detective told the inquest no one had been charged with the killing. (Lost Lives 386 f.)