A) They can't be tried on 'US soil' because they haven't broken any US laws, most of them haven't ever stepped foot in America.
Also, prior to the concentration camp being created in Guantanamo, the US had no problem prosecuting suspected terrorists & placing them in federal prisons.
B) Where is this evidence that released detainees have gone on to be involved in the Iraqi insurgency?
I haven't seen any report of that. But, to be honest, if I'd have been released from a concentration camp after being illegally detained for no good reason, I'd certainly be looking for ways to retaliate against my captors.