A question about the military tribunals

Aside from the complete farce and disgrace that they are, I was taken aback by this brief blurb in an article about how Bin Laden't driver will not be freed after he serves his sentence.

"The Pentagon also is pursuing cases in coming months against two detainees who allegedly killed and injured U.S. troops on the battlefield in Afghanistan. Omar Khadr, who was arrested when he was 15 years old after he allegedly killed a U.S. soldier with a grenade, is expected to face trial at Guantanamo Bay in October. "

http://www.washingtonpost.com/wp-dyn/content/story/2008/08/09/ST2008080900876.html

How can we charge a fighter in the field of battle? It's war. Should our own soldiers be arrested and held indefinitely before given a sham trial.. only to never be released? Overlooking the 'enemy combatant' status, how can a participant in war be charged for fighting (not to mention, against an invader)?