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Can the U.S. kill an American citizen without charge or conviction?

Is it legal for the federal government to kill a U.S. citizen overseas, someone who has never been charged or convicted of a crime? Civil liberties groups are condemning the killing of Anwar al-Awlaki, but many legal scholars say it is fully justified.

No U.S. court has ever weighed in on the question, because judges consider these sorts of issues exclusively matters for the president. 

Anwar al-Awlaki's father, Nasser, with the help of the ACLU, sued President Obama, Defense Secretary Robert Gates, and CIA Director Leon Panetta a year ago, when it became clear that the U.S. was targeting al-Awlaki. But Judge John Bates threw the case out, ruling that federal courts were in no position to evaluate whether someone was a terrorist whose activities threatened national security and against whom deadly force could be justified.

The ACLU lawyer who handled the case, Jameel Jaffer, said Friday the killing of al-Awlaki was a violation of both U.S. and international law.

"The government's authority to use lethal force against its own citizens should be limited to circumstances in which the threat to life is concrete, specific and imminent," Jaffer said. "It is a mistake to invest the president, any president, with the unreviewable power to kill any American whom he deems to present a threat to the country."

But Kenneth Anderson, an international law scholar at American University's Washington College of Law, said U.S. citizens, who take up arms with an enemy force, have been considered legitimate targets through two world wars, even if they are outside what is traditionally considered the battlefield.

"Where hostiles go, there is the possibility of hostilities," Anderson said. "The U.S. has never accepted the proposition that if you leave the active battlefield, suddenly you are no longer targetable."

Robert Chesney, an expert on international law at the University of Texas School of law, concluded in a recently written law review article that al-Awlaki could be legally killed "if he is in fact an operational leader within AQAP, as this role would render him a functional combatant in an organized armed group."