There are lots of examples of US and Australian forces mistreating Japanese POW's. War Without Mercy by John Dower has tons of examples. Japanese were depicted as subhumans to US soldiers and they acted accordingly. This was a mistake as Dower points out that Japanese forces had almost no training concerning what to do when captured. The shock and degradation of capture left them quite willing to cooperate when appropriate numbers of Japanese speaking interpreters were available.
But all this is a separate issue from what the OP was talking about. I think the camps and property siezures were a great injustice and in no way militarily necessary. Sure maybe a small number of camps to isolate the small percentage of Japanese-Americans who actually did something treasonous, and maybe a few of their family members too, but even in this case their property should have been placed in trust or a compensation fund established to get them back on their feet when the war was over.
What I never understood was the Nisei Battalions. If American citizens of Japanese descent were considered so high a security risk that they couldn't be trusted to go on living their mundane civilian lives, why would you draft them and expect them to fight? Why did the Nisei consent to be drafted and fight for a country that had deprived them of their property and freedom? If they resisted, what could the US govt do? Send them to camps? Oh wait, they are already there. Even so, most Nisei accepted the draft and fought bravely for the US.
But maybe mistreatment and executions happen late in the war. The Nisei Battalions hear about this and decide to defect, setting up a stronghold in the Italian alps with the help of German troops. Mussolini decides to move there before he is deposed....