Sources to NBC News are reporting Samir Khan, editor of Inspire Magazine, is another American citizen that was killed in the air strike in Yemen, along with Anwar al-Awlaki. NBC's Bob Windrem reports.
By Pete Williams, NBC News justice correspondent
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 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 Barack Obama, Defense Secretary Robert Gates and CIA Director Leon Panetta a year ago, when it became clear that the U.S. was targeting the younger al-Awlaki. But U.S. District 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 the use of deadly force could be justified.
"This court recognizes the somewhat unsettling nature of its conclusion -- that there are circumstances in which the executive's unilateral decision to kill a U.S. citizen overseas is 'constitutionally committed to the political branches' and judicially unreviewable," Bates said, quoting an earlier decision on a similar issue.
The ACLU lawyer who handled the case, Jameel Jaffer, said Friday that the U.S. program that targeted 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. 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," Jaffer said.
President Obama says the killing of radical, American-born cleric Anwar Al-Awlaki in Yemen is a "major blow to al-Qaida's most active operational affiliate."
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. The U.S. has never accepted the proposition that if you leave the active battlefield, suddenly you are no longer targetable," Anderson said.
In early 2010, the director of national intelligence, Dennis Blair, told a congressional hearing that the U.S. was prepared to kill Americans affiliated with al-Qaida, without mentioning al-Awlaki by name.
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"If we think that direct action will involve killing an American, we get specific permission to do that," by which he meant authority from the executive branch, not the courts.
Blair said the military and intelligence agencies had authority to kill U.S. citizens abroad who were engaged in terrorism if their activities threatened Americans. Since then, U.S. officials have said that al-Awlaki's role in al-Qaida in the Arabian Peninsula (AQAP) had shifted from propagandist to operational tactician and strategist.
The State Department's senior legal adviser, Harold Koh, plainly stated last year the Obama administration's view that it had authority to undertake drone attacks in countries where al-Qaida operatives were located.
Radical cleric influenced many plots, US says
"The U.S. is in armed conflict with al-Qaida as well as the Taliban and associated forces in response to the horrific acts of 9-11 and may use force consistent with its right to self-defense under international law," Koh said in a speech to a Washington legal symposium.
Though he did not specifically address the issue of targeting Americans, many legal scholars believe his speech was an implicit statement that U.S. citizens could be legitimate targets.
One of al-Qaida's most influential leaders - Anwar al-Awlaki - has been killed, according to officials in the United States and Yemen. Authorities have confirmed that the radical Islamist cleric died in an airstrike this morning in Northern Yemen. ITN's Sejal Karia reports.
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Robert Chesney, an expert on international law at the University of Texas School of Law, concluded in a recent 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."
Anderson, of American University's law school, said it's important to note that al-Awlaki was not targeted because of his role as an al-Qaida propagandist.
"The U.S. is not justifying this on the basis that it's going after him for incitement. He was being targeted because he had gone operational," Anderson said, adding that he believed the killing was entirely legal.
"My view of this targeted killing is straightforwardly, congratulations, Mr. President," he said.