For there to be a tribunal, they must break the law as it is written. As Iraq is not signatory to the Hague and Geneva convention, they are not protected by it.

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Jones:- We're going to teach them climbing, abseiling, canoeing, archery, shooting...

Interviewer:- Shooting! That's a bit irresponsible isn't it?

Jones:- I don't see why, they'll be properly supervised on the range.

Interviewer:- Don't you admit that this is a terribly dangerous activity to be teaching children?
You're equipping them to become violent killers.

Jones:- Well, you're equipped to be a prostitute but you're not one are you?

Slight correction to the above. I was slightly off in my explanation. It is only the HC (the Hague Convention establishes weapons useage) that forgoes all rights to those not signatory. As per Articles 1 and 2 of the 3GC, non-signatory states are covered in some cases, But as per article 2 of the Third Geneva Convention, the party(that’s us) will remain bound until the non-signatory (that’s the insurgents) no longer acts under the strictures of the convention.

So the second they beheaded their captives, they lost all rights under 3GC.

But then again, you also have to take into account that they are not an organized state military. So some would say that they never fell under the GC.

__________________
Jones:- We're going to teach them climbing, abseiling, canoeing, archery, shooting...

Interviewer:- Shooting! That's a bit irresponsible isn't it?

Jones:- I don't see why, they'll be properly supervised on the range.

Interviewer:- Don't you admit that this is a terribly dangerous activity to be teaching children?
You're equipping them to become violent killers.

Jones:- Well, you're equipped to be a prostitute but you're not one are you?