I suspect this sort of thing was likely more commonplace than the history books are willing to admit...there are accounts of Canadian soldiers executing SS and even Wehrmacht prisoners out of hand following the discovery of the bodies of Canadian prisoners who had been shot in the back of the head at the Abbe Ardenne by 12th SS Panzer, Hitler Jugend, in Normandy.
My father was there when that happened. He told me once that on the night of June 6 or 7, some of his friends went out on a patrol. Someone asked him if he wanted to come along and he said "no", but someone else said he'd go. They were all found the next day or so with their hands tied and they'd been shot.
The was some speculation that perhaps the little embroidered "black devil" on their uniform sleeves had caused them to be shot as Commandos under Hitler's "Fuehrer Order" that dictated that all special service troops and paratroopers were to be shot on the spot. Anyway, they knew it was the Hitler Jugend guys that did it. 64 Royal Winnipeg Rifles were shot in Normandy, according to the monument if I remember correctly in Winnipeg, from the 6th to the 8th, as prisoners. They all had the little devil embroidered on their uniform sleeves, because their unit was nicknamed the "little black devils". I grew up wearing that uniform playing soldiers, but now I believe it is on display in the Winnipeg Rifles Museum in Winnipeg. It went to the Museum after he died, but I was already living down here and have not seen it, although I have some photos of the display that were sent to me. When I told my father sometime in the '70's or '80's that the commander of that unit, Kurt Meyer, had supposedly been hung (according to some book I read at the time) after the war, Dad just said "he had it coming." Turns out, that information was actually wrong and Meyer's sentence was commuted to prison time. But at the time, I thought that they'd hung Meyer because this old book had said so. Probably just as well, because of me Dad believed that Meyer was hung and was happy with that. Had I had an Internet to fast-check my facts, I'd have had to tell him that Meyer got off with prison time and that would have upset the old man.
At about the age of 12 or 13, I watched the movie "The Battle of the Bulge" at the Brandon Drive-in with my dad. When they shot all the American prisoners, I cursed the Germans. My father commented that "the Germans weren't the only ones who shot prisoners."
Later in life, I asked my dad about the comment. He told me that after the executions of Canadian prisoners in Normandy, it was difficult for S.S. to surrender to the Winnipeg Rifles. I do not know if other Canadian Units had the same SOP, but I know from both my Dad's comments and books I have read that this was probably true of the RWR. I asked my Dad if he had ever shot any prisoners, and he hesitated a bit, then said; "No, I never did. But I did stand guard once at the end of a little lane while a couple of my friends took some of those Hitler Youth S.S. boys down the path to let them try to escape."
Dad was a virtual fountain of information about the war if you could pry it out of him, and I spent until the day he died working on it. Once, at the Brandon Strand Theatre watching "The Longest Day", when the scene where Hans Priller and his wingmen fly above the Sword and Juno beaches strafing the landing troops, my Dad leaned over to comment to me, but due to some latent emotion spoke rather loudly and said, "I saw him!" Later, when the movie ended, people sitting around us started asking Dad if he had been there, and he got his 15 minutes of fame as people came to shake his hand and just touch his arm or say something to him. He had a strange grin on his face the rest of the day.
Around 1978 or so, I finally read Cornelius Ryan's "The Longest Day" on which the movie was based. At the end of the book, it tells a little bit about what happened to the people featured in the book. Priller, the German airman, and his wingman had been well regarded in Germany for having flown above the invasion beaches. Probably the only German planes above the beaches that day. If I remember correctly, he got a job high up in Lufthansa or something, and took that wingman with him. I told my Dad about it, and his comment was, "Good, he deserved it. He was a brave man."
So Dad was not always predictable in the way he'd respond to things. He sure hated the S.S. though.
Photo; My Dad died in 1994. This photo of him is from about 1989, with the 1928/A1 Thompson he liked so much. (He used a Bren gun during the war.) The gun is now in the Evergreen Machine Gun museum in Belmont, Manitoba. I always used to tease him that he reminded me of Warren Oates in "Dillinger"...and you know, thinking about it...he just sorta did.