Good old SS. 1st SS Division recently returned from the eastern front where murder of prisoners was common.
Turned out bad for them as word of the massacre got out the GI's would just shoot them on sight. Officers just looked the other way.
More common than you know. My Dad (Normandy veteran) told me that Americans also killed prisoners. My Uncle, also a veteran of France and Germany, confirmed it.
As a veteran of Vietnam myself I can't say I ever saw a prisoner being killed but there were certainly stories of it going around among the troops. To those who have not been there it would do well to remember the old saying -
"War is hell...but COMBAT is a M**********R"
You really have no idea.
43 Germans were sentenced to death for Malmedy, but irregularities in the trial (including some credible claims of torture) vitiated the trial, and all had their sentences commuted. The last was released in 1954.
The logic of the massacre was coldly practical - the plan depended upon speed and the armored spearheads felt they could not afford the time to process prisoners.
I’m not sure anyone received the punishment for it the act deserved.