Your argument basically boils down to:
Well, despite the evidence and the logic, you can't prove that Bush authorized torture, so he categorically did not do so.
This is fallacious. Either Bush or those in his cabinet - Cheney - authorized torture. Bush either did it himself personally or authorized others to make executive decisions for him. Either way, those responsible should be investigated, tried, and if found guilty, punished, for breaking the law.
There is ample evidence that the administration knew they were engaging in torture - in some of their memos they forgot to use the EI dodge and plainly called it that. See:
As for the jurisdiction issue, I would remind you that the same treaty Congress extended to cover non-US sites in 1994 already
prohibited torture on US sites. The location of the torture was immaterial.
Additionally, evidence has emerged which strongly suggests that Cheney ordered the torture to take place in large part to attempt to establish a link between AQ and Iraq and justify the war; NOT to stop a 'ticking time bomb' or any of that bullshit. See:
May 21, 2009
Cheney and the Iraq-Torture Link
By Joe Conason
Cheney has since admitted that there was no link. But there is little doubt that he tortured people to try and establish one.
I will accept your premise that it is difficult to prove Bush's complicity in this, though he doubtlessly was complicit, due to his protected role as President. Cheney, however; I think you would have a much harder time making the case that Cheney did not personally know of and approve torture of prisoners in US custody. And he should be investigated, tried, and if found guilty, punished for this, no matter what he claims the reasons were.
There is no reason why anyone who wishes to shouldn't try to obtain proof that Mr. Bush authorized torture, but there would actually have to be something that he signed, and clearly you don't have it. Frankly, I doubt that he did authorize torture. You say, "you would have a much harder time making the case that Cheney did not personally know of and approve torture of prisoners in US custody," but I don't have to prove that and neither do Mr. Bush or Mr. Cheney. If no one can prove that they authorized it, then they cannot be tried in a real court of law. I agree, though, that if anyone, no matter who, authorized torture (not agressive interrogation), and if, in fact, it violates a law, they should be prosecuted. If torture (not agressive questioning) is not illegal, it should be made illegal. However, to my way of thinking, this is simply more of slinging around unsubstantiated accusations about everything under the sun against the former president . When you have some evidence, then you, or those who think like you, can go to court. Right now you do not.