It Has been done, If a American is found and charged with being a terrorist, A military court, should be convened, The person charged publicly. If found and proven guilty by our laws , a Warrant is issued. US Citizenship striped under the Constitution . If he can be found and arrested in the US Fine If he is not and in a terrorist area Drones can and should be used. Never on US soil.
Janet Reno proved that point with how many killed in wacko and Ruby Ridge And we did not have drones yet. There uses will only escalate if unchecked.
One thing is certain if he is arrested and brought to trial in The USA He will lawyer up and it will take years to get it done, That's the reason I say a Military Trial. and given a Lawyer. and Then A bullet.