How do you know that there has not been a tribunal and that they have not been deemed "illegal combatants"? These things are not required to be done in public.
Not in public , but there are certain nominated parties that must be informed of any developments , in this case the Red Cross and the detainees country of origin , the country they were originally detained in whether it is a country involved in the conflict or a neutral third country , and the country in which they are detained and any country they have been transfered through while in detention .
Complicated things laws arn't they , is that why you have a problem with them ?

Yes, but if they have been found to be illegal combatants, then holding them in isolation and interrogating them is not a violation of any law that I am aware of.
There are also lots of stipulations on interrogation , holding in isolation is also not allowed unless under specific circumstances .