The US has argued that Anwar al-Awlaki had joined the enemy.
THE killing of Anwar al-Awlaki, a US citizen hit by a missile fired from a drone operated by his own government, has reignited a difficult debate over terrorism, civil liberties and the law.
The Obama administration had long argued that al-Awlaki, 40, had joined the enemy in wartime, shifting from propaganda to an operational role in plots against the US, and last year it decided that he could be targeted for capture or death like any other al-Qaeda leader.
It was unclear whether the same formal determination had been made about another radicalised American killed in the same strike, Samir Khan.
Some civil libertarians questioned how the government could take a US citizen's life based on murky intelligence and without an investigation or trial, claiming that hunting and killing him would amount to summary execution without the due process of law guaranteed by the constitution.
With the help of the American Civil Liberties Union, al-Awlaki's father, Nasser al-Awlaki, a former agriculture minister and university chancellor in Yemen, had challenged the administration's decision to place his son on the kill list, but the lawsuit was thrown out of federal court in Washington.
Yesterday, Jameel Jaffer, the ACLU's deputy legal director, said the government's targeted killings violated US and international law. ''As we've seen today, this is a program under which American citizens far from any battlefield can be executed by their own government without judicial process, and on the basis of standards and evidence that are kept secret, not just from the public, but from the courts,'' Mr Jaffer said.
Robert Chesney, a law professor at the University of Texas who specialises in national security law, said he believed the killing was legal. But he said it was ''plenty controversial'' among legal specialists, with experts on the left and on the libertarian right deeply opposed to targeted killings of Americans.
The administration's legal argument in the case of al-Awlaki, Professor Chesney said, appears to have three elements: al-Awlaki posed an imminent threat to the lives of Americans; he was fighting with the enemy in the conflict; and there was no feasible way to arrest him.
But critics note that the Fifth Amendment to the US Constitution states that no American shall be ''deprived of life, liberty, or property, without due process of law''. In ordinary circumstances, that requires a trial and conviction.
No public legal process led to al-Awlaki becoming, early in 2010, the first US citizen to be placed on the CIA's list of al-Qaeda-linked terrorists to be captured or killed. Officials said every name added to the list undergoes a careful, if secret, legal review.
Because of al-Awlaki's citizenship, the decision to add him to the target list was approved by the National Security Council as well.
One factor is that the precedents mainly involve the military detention of Americans who sided with the enemy during World War II, not the killing of Americans in an unconventional war. ''What's tricky here is that many people don't accept that this is a war,'' Professor Chesney said. The US-educated son of a US-educated Yemeni technocrat, Anwar al-Awlaki embodied the puzzle of radicalisation: How did a US citizen come to call for mass murder, in eloquent English, mastering the megaphone of the internet?
Al-Awlaki's religious justifications for violence against his fellow Americans had a profound impact on a small number of young Muslims in the US, Canada and Britain. In a score of plots since 2006, investigators discerned al-Awlaki as an important radicalising influence, his written, audio and video sermons stored on hard drives, emailed among conspirators and treated as an authoritative clerical imprimatur for their deeds.
At least since 2009, US intelligence officials asserted, he had taken on a more significant role in al-Qaeda in the Arabian Peninsula, the Yemen-based branch of the terrorism network. Notably, they said he had helped recruit and train Umar Farouk Abdulmutallab, the young Nigerian who tried to blow up an airliner headed for Detroit on Christmas Day in 2009 with a bomb sewn into his underwear.
Whatever the details of his hands-on participation in terrorism, al-Awlaki left no doubts about where he stood, certainly since November 2009, when he praised Nidal Malik Hasan, the US Army major accused of killing 13 people at Fort Hood, as a hero.
The latest issue of Inspire, the English-language online magazine that he and Khan contributed to and may have edited, promised that ''coming soon'' would be an article by al-Awlaki titled ''Targeting the Populations of Countries That Are At War with the Muslims.''
Al-Awlaki was born in 1971 in New Mexico.He moved to Yemen with his parents at the age of seven and attended school in the Muslim country, where he later told friends he had been thrilled by tales of Yemeni men fighting the Russians in Afghanistan.
At 19, he was sent back to the US to attend university. He completed an engineering degree, but by then had discovered his knack for preaching in the little mosque in Fort Collins. He became the imam in mosques in Denver, San Diego and the Virginia suburbs of Washington, where he had contact with at least two of the future September 11 hijackers.
Though he denounced the September 11 attacks, he was angered by what he thought was anti-Muslim government investigations in the months that followed, and he moved to London and eventually to Yemen, where he was imprisoned in 2006 and 2007.
He created an English-language website, blog and Facebook page that drew tens of thousands of visitors, putting out a message that grew steadily more approving of anti-Western violence, culminating in the endorsement of Hasan's shooting rampage.