How were the World War II POWs were treated in the USA?
There was a joke in the German military during World War II which said, if there is ever a world war, get on the side fighting the United States and then surrender to them, and you'll be sure to come home alive. While this wasn't a joke you said to the wrong people, it was generally accurate.
While POWs in Japan's empire or in the Soviet Union had to literally fear for their lives, and depending on country of origin, possibly in Germany too, those captured and actually imprisoned by Britain or the US were all but guaranteed to survive. The worst that would happen to you is you would be forced to do agricultural work (the US was short of farmworkers during the war), but even then, when working on family farms, the family would be required to provide a meal.
My Mother-in-law was a young child in Kansas dring the war, and they had a group of five German POWs who regularly worked for their father in planting and harvest time. Kids were told to stay out of the room when the POWs were eating lunch, but my Mother-in-law snuck in one time, a German saw her and immediately burst into tears, no doubt thinking of his own daughter back home, who he was eventually returned to once the war ended.
Overall, Prisoners of War who were brought back to the United States were treated very well indeed. The US had plenty of food for everyone and they had not really been hurt at home by the war. That meant they did not have the same sort of problems feeding prisoners or the same kind of hate for the prisoners that other countries might have had.
There are numerous stories of POWs being allowed to work relatively unsupervised on farms near to their camps, for example. And there is a famous case in which black troops rioted near Seattle because the prisoners were treated better than they were by the public. (The POWs were allowed to do things like having chaperoned trips to bars and movies.)
Outside of the one POW killed in the Seattle riot, the only incidents I have heard of that involved POWs getting killed involved things like true believer Nazis killing POWs who were seeming to like the US too much.