If you're a friend and supporter of Joe's, you testify that he's a good man in the court (or United Nations), if you elected a government that gave Joe the weapon, if you profited from Tim being killed, then yes, you're also guilty. You've basically delegated the dirty job of "finding cheap oil by any means necessary so I can have an easier life" to Joe.
I'm not saying you should be the world's police; what I'm saying is if you profit from others being oppressed (so the oppressor can sell you oil cheaper so you can have a better life), it's your duty as a human being to try to change things for your brother.
Of course, if you're not profiting from that oppression, or aren't supporting the oppressor, then it's NOT your duty but still it would be nice to intervene.
> ... don't shift the blame where it isn't due.
Not at all. Those dictators are guilty of all those crimes. No one's arguing against that.