Of the scores of people dubbed terrorists who have been targeted by American military drone strikes, three men -- all killed in the fall of 2011 -- were U.S. citizens.

And their lives illustrate the complexity of the issue, recently brought to light amid a newly discovered government memo that provides the legal reasoning behind drone strikes on Americans.

Anwar al-Awlaki and Samir Khan were killed by a missile strike in Yemen on Sept. 30, 2011, while al-Awlaki’s son, Abdulrahman, was killed in the country just weeks later. 

Since the attacks, family members have called the deaths unjust and sued the U.S. government, calling the killings unconstitutional.

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Anwar al-Awlaki, born in New Mexico, became well known for his fiery anti-American sermons posted throughout the Internet.

Samir Khan, who'd lived in both New York and Charlotte, N.C., produced a magazine called “Inspire” that became known for its extreme jihadist views.

But the most controversial drone strike took place on Oct. 14, 2011, when 16-year-old Abdulrahman was killed by U.S. forces.

Family of the Denver-born teenager say he had no ties to terrorist organizations and was unjustly targeted because of his father.  

Nassar al-Awlaki, grandfather of Abdulrahman and father to Anwar, said he tried to protect his grandson as Anwar al-Awlaki’s profile grew.

In December, Nassar al-Awlaki told CNN, “In Anwar it was expected because he was under targeted killing, but how in the world they will go and kill Abdulrahman. Small boy, U.S. citizen from Denver, Colorado.”

Nassar al-Awlaki said his grandson snuck out of their Yemen home one night, leaving a note for his mother saying he would return in a few days. The boy never returned, killed instead while eating at an outdoor restaurant.

“Since the issue regarding Anwar came, I tried to insulate the family of Anwar from everything, regarding this matter,” Nassar al-Awlaki told CNN. “I took care of him, and suddenly after 2 year absence from his father, he decided to go to our government in Yemen to seek information from his father. That was the only reason he went, and he did not tell us.”

The Obama administration has remained mostly mum regarding Abdulrahman's death, and at times has struggled to explain it. 

Read more: Memo details legal case for drone strikes

"I would suggest that you should have a far more responsible father if they are truly concerned about the well-being of their children," former White House spokesperson Robert Gibbs said to a gaggle of reporters in October. "I don't think becoming an al-Qaeda jihadist terrorist is the best way to go about doing your business."

During his presidential campaign, Republican Rep. Ron Paul criticized the killing of Anwar al-Awlaki, saying: “Al-Awlaki was born here, he is an American citizen. He was never tried or charged for any crimes. No one knows if he killed anybody. ... But if the American people accept this blindly and casually that we now have an accepted practice of the president assassinating people who he thinks are bad guys, I think it's sad.”

Anwar al-Awlaki’s ties to the United States go back to his father Nassar, who came to the country to earn a master’s degree. His son was born in New Mexico, and though the family returned to Yemen, Anwar al-Awlaki came back to the U.S. for college, eventually becoming an iman.

Shortly after the Sept. 11, 2001, he became a popular spokesman for moderate Islam, and was often used to juxtapose perceptions that Islam is a religion that spreads hate.  But less than a decade later, he was hiding in Yemen as a name on the CIA's kill list.

“I eventually came to the conclusion that jihad against America is binding upon myself just as it is binding on every other Muslim,” he said in an audio message in March 2010.    

Conversely, Khan was never interested in the peaceful side of Islam. The New York Times reports that as a teen, Khan’s attraction grew exponentially to militant sites on the Internet after 9/11. Parental concerns and intervention from community leaders proved unsuccessful. Khan was 25 when he died in Yemen.

In July 2012, Samir Khan’s mother, Sarah, joined Nassar al-Awlaki in a lawsuit against four senior national security officials.

“I don’t really necessarily agree with some of the things Anwar said against the United States, but does that mean they should kill him outside the law?” asked Nassar al-Awlaki.

Update: A fourth American-born citizen, Kamal Derwish, was killed by predator drone in Yemen in 2002. Derwish was not the primary target of the strike, but was riding in an SUV carrying an al-Qaida leader.

A Vietnamese immigrant has been charged in New York over an alleged role in helping al-Qaida in Yemen.

Minh Quang Pham was arrested in Britain. He is accused of traveling to Yemen to train with members of al-Qaida in the Arabian Peninsula, or AQAP. 

Pham is also accused of helping the group with its online propaganda efforts. Investigators said he was in Yemen from December 2010 through July 2011.

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See the original report at NBCNewYork.com

Sources familiar with the case said he met with numerous leaders of AQAP in Yemen, including the terror group's then leader, Anwar al-Awlaki, and Samir Khan, editor of its English-language magazine "Inspire," and took a loyalty oath. Both Americans-turned-terror leaders were killed in a drone strike last September.

"The defendant not only pledged an oath to al-Qaida in the Arabian Peninsula, and received military training from AQAP, he also helped design and disseminate its propaganda,"New York FBI Assistant Director-in-Charge Janice K. Fedarcyk said.

Security officials have said AQAP has become the leading overseas terror threat to the U.S. 

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Two underwear bomb plots, including one that targeted a Detroit-bound jetliner, as well as a plot to bomb cargo planes in 2010, originated in Yemen.

As for Pham, the court papers said he played a role in creating online propaganda for AQAP. He is charged with conspiracy to provide material support to a foreign terrorist organization. 

Jonathan Dienst is WNBC's chief investigative reporter. Shimon Prokupecz is WNBC's investigative producer.

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Updated at 10:05 a.m. ET: LONDON -- Two U.S. reports published Tuesday provide significant insights into President Obama’s personal and controversial role in the escalating covert U.S. drone war in Pakistan, Yemen and Somalia.

In a major extract from Daniel Klaidman’s forthcoming book Kill Or Capture, the author reveals extensive details of how secret U.S. drone strikes have evolved under Obama – and how the president knew of civilian casualties from his earliest days in office.

The New York Times has also published a key investigation exploring how the Obama Administration runs its secret 'Kill List' – the names of those chosen for execution by CIA and Pentagon drones outside the conventional battlefield.

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The Times' report also reveals that President Obama "embraced" a broadening of the term "civilian", helping to limit any public controversy over "non-combatant" deaths.

As the Bureau's own data on Pakistan makes clear, the very first covert drone strikes of the Obama presidency, just three days after he took office, resulted in civilian deaths in Pakistan. As many as 19 civilians – including four children – died in two error-filled attacks.

Until now it had been thought that Obama was initially unaware of the civilian deaths. Bob Woodward has reported that the president was only told by CIA chief Michael Hayden that the strikes had missed their High Value Target but had killed "five al Qaeda militants."

Read more stories from The Bureau of Investigative Journalism

Now Newsweek correspondent Daniel Klaidman reveals that Obama knew about the civilian deaths within hours. He reports an anonymous participant at a subsequent meeting with the president: "You could tell from his body language that he was not a happy man." Obama is described aggressively questioning the tactics used.

Yet despite the errors, the president ultimately chose to keep in place the CIA’s controversial policy of using "signature strikes" against unknown militants. That tactic has just been extended to Yemen.

'Covert' US drone operation is mapped on Twitter

On another notorious occasion, the article reveals that U.S. officials were aware at the earliest stage that civilians – including "dozens of women and children" – had died in Obama’s first ordered strike in Yemen in December 2009. The Bureau recently named all 44 civilians killed in that attack by cruise missiles.

'I'd have to go to confession'
No U.S. officials have ever spoken publicly about the strike, although secret diplomatic cables released by Wikileaks proved that the U.S. was responsible. Now Klaidman reveals that Jeh Johnson, one of the State Department’s senior lawyers, watched the strike take place with others on a video screen:

"Johnson returned to his Georgetown home around midnight that evening, drained and exhausted. Later there were reports from human-rights groups that dozens of women and children had been killed in the attacks, reports that a military source involved in the operation termed “persuasive.” Johnson would confide to others, “If I were Catholic, I’d have to go to confession.”

Klaidman describes a world in which the CIA and Pentagon constantly push for significant attacks on the U.S.’s enemies. In March 2009, for example, then Chairman of the Joint Chiefs of Staff Mike Mullen reportedly called for the bombing of an entire training camp in southern Somalia in order to kill one militant leader.

Pakistan official: US drone strike hits mosque; 10 killed

One dissenter at the meeting is said to have described the tactic as "carpet-bombing a country." The attack did not go ahead.

Obama is generally described as attempting to rein back both the CIA and the Pentagon. But in the case of Anwar al-Awlaki – "Obama’s Threat Number One" – different rules applied.

According to Klaidman, Obama let it be known that he would consider allowing civilian deaths if it meant killing the U.S.-Yemeni cleric. "Bring it to me and let me decide in the reality of the moment rather than in the abstract," an aide recalls him saying. No civilians died that day, as it turned out.

In its own major investigation, the New York Times examines the secret US 'Kill List' – the names of those chosen for death at the hands of US drones. The report is based on interviews with more than 36 key individuals with knowledge of the scheme.

Drone spotting at secret Nevada base stirs up debate

The Times' report says:

"[Obama's] first term has seen private warnings from top officials about a 'Whac-A-Mole' approach to counterterrorism; the invention of a new category of aerial attack following complaints of careless targeting; and presidential acquiescence in a formula for counting civilian deaths that some officials think is skewed to produce low numbers."

It is often been reported that President Obama has urged officials to avoid wherever possible the deaths of civilians in covert U.S. actions in Pakistan and elsewhere. But reporters Jo Becker and Scott Shane reveal that Obama "embraced" a formula understood to have been devised by the Bush administration:

"Mr. Obama embraced a disputed method for counting civilian casualties that did little to box him in. It in effect counts all military-age males in a strike zone as combatants, according to several administration officials, unless there is explicit intelligence posthumously proving them innocent."

So concerned have some officials been by this "false accounting" that they have taken their concerns direct to the White House, according to the New York Times.

Photos document alleged US drone strike victims in Pakistan

The revelation helps explain the wide variation between credible reports of civilian deaths in Pakistan by the Bureau and others, and the CIA’s claims that it had killed no "non-combatants" between May 2010 and September 2011 – and possibly later.

The investigation also reveals that more than 100 U.S. officials take part in a weekly "death list" video conference run by the Pentagon, at which it is decided who will be added to the U.S. military’s kill/ capture lists. "A parallel, more cloistered selection process at the CIA focuses largely on Pakistan, where that agency conducts strikes," the paper reports.

But according to at least one former senior administration official, Obama’s obsession with targeted killings is "dangerously seductive." Retired admiral Dennis Blair, the former US Director of National Intelligence, told the paper that the campaign was:

"The politically advantageous thing to do — low cost, no US casualties, gives the appearance of toughness. It plays well domestically, and it is unpopular only in other countries. Any damage it does to the national interest only shows up over the long term."

 

Clarification: An earlier version of this story said that President Obama "personally authorized the broadening of the term 'civilian'" and attributed the redefining of "civilian" to his administration. However, The Bureau of Investigative Journalism now understands that the Obama administration instead embraced a pre-existing policy introduced under President George W. Bush. The Bureau apologizes for this error.

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The spy who helped Western intelligence agencies thwart a plot to bomb a U.S.-bound airliner was a British national of Middle Eastern origin, sources tell NBC News.

The sources, speaking on condition of anonymity, also say that British intelligence was "heavily involved" in recruiting the spy, who has not yet been identified publicly, and penetrating the plot by al-Qaida in the Arabian Peninsula to detonate a new, more sophisticated underwear bomb aboard a U.S. jetliner.

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A senior U.S. counterterrorism official, also speaking on condition of anonymity, would say only that multiple friendly security services were involved in the operation. Saudi Arabia's counterterrorism operation also were involved, other U.S. officials have told NBC News.

U.S. and British officials have long reported that AQAP has wanted to recruit Muslims with Western passports to carry out attacks like the one revealed this week. As an example, the officials cited AQAP’s recruitment of Umar Farouk Abdulmutallab, who failed in the Christmas Day 2009 attempt to bring down Northwest Airlines Flight 253 over Detroit.

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U.S. officials have said previously that the bomb -- a refined version of an “underwear bomb” used in two previous failed terror plots -- was driven out of Yemen by the insider into Saudi Arabia. It is now in the hands of U.S. bomb experts at the FBI labs in Quantico, Va., where experts have been examining it for a week, the officials said. The infiltrator also is safely out of Yemen.

The insider also provided information that allowed the U.S. to launch a Predator drone strike that killed AQAP's operations chief, Fahd al-Quso, senior U.S. officials told NBC News on Tuesday.

Evan Kohlmann, NBC counterterrorism analyst, said he found earlier reports that the spy  was a Saudi national not very credible.

“AQAP was going to give a suicide bomb to someone with a Saudi passport?” Kohlmann asked rhetorically. “AQAP has been looking for bombers with Western passports, not those who would raise suspicions.”

He noted that Abdulmutallab, who tried to detonate an earlier version of the underwear bomb aboard the Northwest flight, better  fit the profile AQAP was looking at: a young upper class college student with a Nigerian passport and a multiple-entry U.S. visa. A British national would attract even less attention, he said.

Robert Windrem is a senior investigative producer for NBC News; NBC News Justice Correspondent Pete Williams and Jonathan Dienst of WNBC-TV contributed to this report.

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Just days before the news broke about the CIA's takedown of a plot involving a sophisticated new underwear bomb, al-Qaida’s affiliate in Yemen publicly boasted that it had vastly expanded and improved its capabilities for making such devices.

That boast -- contained in a largely overlooked passage of Inspire, the online propaganda organ of al-Qaida in the Arabian Peninsula (AQAP) -- has fueled concerns that there may be other versions of the seized device and more bomb makers assembling them, according to U.S. security officials and members of Congress who have been briefed on the case.

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"They have a team of engineers, scientists and doctors. It's a little spooky,"  said Rep. Mike McCaul, R-Texas, a member of the Homeland Security Committee who was briefed this week on the intelligence operation that U.S. officials say thwarted an AQAP plot to bomb a U.S.-bound airliner. "In my view, it’s very likely they have produced more of these."

One hint at the expansion of AQAP's bomb-making capabilities can be found in passages in an article entitled "Wining on the Ground," found on the 57th page of the latest 59-page edition of Inspire, released by AQAP last weekend.

In 2009, AQAP had only a "very modest and small laboratory in a rural area" to make bombs, the author of the article –identified as Yahya Ibrahim -- wrote.

That was the year AQAP dispatched a suicide bomber to use a chemical underwear bomb to attempt to assassinate Prince Mohammed bin Nayef bin Abdul Azizbin, director of Saudi Arabia’s counterterrorism program, and later deployed another operative from Nigeria to try to blow up a U.S. airliner bound for Detroit. Neither device detonated properly, though the bomber in the first attack was killed.

But now, after obtaining “a large deal of chemicals from military laboratories" in a key city in southern Yemen -- "the modest lab has transformed into a modern one," the Inspire article stated.

"Hence, no wearisome measures are taken anymore to obtain the needed large amount of chemicals for explosives," it said. "Also, the operations now do not lack money as before." 

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Lawmakers vow investigation of bomb plot leak 

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This was not the first time AQAP has signaled that its bomb-making capabilities may be greater than U.S. officials have suggested.

In an issue of Inspire in late 2010, the group appeared to mock comments by U.S. officials focusing on the critical role of its top bomb-maker, Ibrahim Hassan Asiri -- who has been widely credited with designing the underwear bombs.

"Isn't it funny how America thinks AQAP has only one major bomb maker?" an article stated. 

Gregory Johnsen, a highly respected Yemen scholar who specializes in AQAP at Princeton University, said the propaganda outlet’s statements are likely true.

"We have to assume that there is not only one bomb-maker," he said. "It makes sense that he (Asiri) is somebody who has taught others" about making such bombs.

Johnsen said that the expansion of AQAP's bomb-making operations would be just one example of the dramatic gains the group has made in the past few years. As a result of the internal chaos in Yemen, and its shrewd exploitation of civilian casualties caused by U.S. air strikes, AQAP has made major advances, Johnsen said.

By U.S. intelligence estimates, the number of AQAP fighters has tripled to more than 1,000. It has also seized swaths of territory in southern Yemen, where it runs its own court system, deploys police officers and provides electricity to some towns, Johnsen said.

U.S. intelligence officials say they have no specific information indicating that other improvised explosive devices (IEDs) similar to the one that was turned over by a CIA informant last month have been produced and possibly spirited out of Yemen.

But John Brennan, President Barack Obama's chief counterterrorism adviser, said Tuesday in an interview with PBS that U.S. officials are taking additional measures "to prevent any other type of IED similarly constructed from getting through security procedures."

At the same time, the U.S. Department of Homeland Security issued new "guidance" calling for enhanced security at foreign airports, including additional pat-downs and random searches, as well as other steps aimed at detecting such bombs.

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