You want the truth?
We can do whatever the hell we want because the people we killed are what the world consider as "Secondary People" They are not equal, they don't sell advertisement slot, and nobody in the west care enough to care about them. And nobody in the West would bat an eyelid when they died a horrible way.
It's like what Nick Nolte said in Hotel Rwanda
The world focus on Power and Money, and if your country did not have neither, then you are dirt, you want to look to the UN to help you? Well, you are either in US camp or in Russia Camp, and if you are stupid enough to go beside either one of those interest, you are stupid enough to get deal with by the UN. This is how UN was set up.
So in what way do you have enough "power" or "money" to put US or Russia or China or UK or France on trial? Nobody care about what you think, you can scream unfair all day long but at the end of the day you are just going to do that until you die and died bitterly in the end.
If you want to bring US to justice? Develop your economy so you can replace us. Otherwise, nobody will listen to you, because your opinion don't worth shit. And I am sorry for that, but that IS the truth. Whether you like it or not.