I researched the US Army's arrival at Dachau as my grandfather "did time" there, though before the camp's liberation in 1945. The troops were aghast at what they found. The pictures don't capture the stench and the sound. I would not use the word "massacre" to describe the US soldier's actions. They had seen their own slaughtered and still felt themselves in hot pursuit of the enemy. Also, they did not want to spend their time dealing with NAZI prisoners who would be a continuing burden -- and detract from their efforts, given limited resources -- to tend and possibly save the innocent. Consider it battlefield triage. Do not be "bothered" at all.
I think you and I are pretty much in agreement here.
I thought the military term was "Summary Execution".