In Australia, under the Foreign Incursions Act for joining guerrilla fighters, the penalty ranges up to a 14-year gaol sentence, but falls short of the death penalty. If the circumstances permitted it, he could be charged with treason under the Commonwealth Crimes Act, which does have the death penalty.
It maybe possible that there are hundreds of Aussies, both military and civilian fighting alongside guerrilla fighters around the world. To have prosecuted Hicks under Australian Law might have opened a can of worms. Someone here made the political decision early on to let the US handle him in which ever way they see fit.
