why were they given such lenient sentences?
First off, I would say this is one of the best war films ever made. The storyline and immersion really has a tremendous effect on the audience. I know in real life the perpetrators were given harsh sentences at first but were eventually commuted to lesser sentences.
Look up Oise-Aisne American Cemetery Plot E. It is the gravesite of over 90 servicemen who were executed for war crimes during World War II for charges of murder and rape. They received death sentences for atrocities committed against victims from Britain, France, Poland, Italy, Algeria, and even some of their own fellow soldiers! It just doesn't make sense why they seem to have sort of a double standard.
Why would the Army be so strict on such atrocities during World War II, but shortly thereafter in Vietnam, become so lenient with things like this?