The recent U.S. killing of al-Qaeda's Anwar al-Awlaki raises some prickly legal questions for President Barack Obama.

There is no question that al-Awlaki, the leader of al-Qaeda in the Arabian Peninsula, posed a threat. He had already been linked to a failed suicide bombing attack on a plane in Detroit, as well as a mass murder in Fort Hood, Texas.

Here's the problem for Obama: al-Awlaki was a U.S. citizen and he was targeted for an extrajudicial killing by the U.S. Central Intelligence Agency. He was executed by a strike from a drone—an unmanned aerial vehicle—in Yemen.

The Straight has already reported that legal groups are trying to have former president George W. Bush tried in Canada for torture that took place while he was in the White House.

Meanwhile, Bush's predecessor, Bill Clinton, has been accused of war crimes in connection with NATO's attack on Yugoslavia and American bombing raids against Iraq, not to mention the deaths of vast numbers of Iraqi children who were deprived of medicine during the 1990s.

One of the lawyers pursuing Bush, Katherine Gallagher of the New York–based Center for Constitutional Rights, told me on September 29 that "there are serious questions about what Barack Obama's administration is doing with the use of drones in Pakistan and beyond."

"We had filed a legal challenge last year against President Obama for the intended targeted assassination of an individual in Yemen," she said just a day before al-Awlaki was killed. "I think there will be continued scrutiny on that."

Following the drone attack, the CCR's executive director, Vince Warren, described it as "the latest of many affronts to domestic and international law".

"The targeted assassination program that started under President Bush and expanded under the Obama administration essentially grants the executive the power to kill any U.S. citizen deemed a threat, without any judicial oversight, or any of the rights afforded by our constitution," Warren said in a news release. "If we allow such gross overreaches of power to continue, we are setting the stage for increasing erosions of civil liberties and the rule of law."

As long as Obama remains in office, he will enjoy diplomatic immunity on any state visit to Canada. But don't be surprised if there are similar calls to arrest him—just as there have been for Bush—if he decides to come to Vancouver after his political career ends.

Last week at the Peter Wall Institute for Advanced Studies fall lecture at the Vogue Theatre in Vancouver, UBC politicial geographer Derek Gregory offered an illuminating history of the drone program. He also raised intriguing legal and ethical questions, which could haunt Obama in the future.

Gregory noted that the U.S. has asserted that it has the right to deploy drones anywhere in the world.

"Human Rights Watch has written to President Obama on how the administration defines the global battlefield," he said. "What is the legal basis for that definition? Do the goals of targeted killing vary from one place to another? Are different criteria used in Yemen and Pakistan?"

He quickly added that while this is obviously of concern to people living in those two countries, everyone should be paying attention.

"It matters for all of us when other states around the world have their own fleets of predators and reapers and demand the same privilege," Gregory stated.

In tracing the history, the UBC academic noted that the drone program was originally targeted at so-called "high-value targets". The first attack occurred in southern Waziristan in Pakistan in 2004, killing a Taliban commander who was described as an "al-Qaeda facilitator", as well as four companions, including a young boy.

In 2007, there were five drone strikes. The number rose seven-fold to 35 in 2008, which was Bush's last year in office.

According to Gregory, Obama authorized a doubling of the CIA's fleet of predator drones "so that it now contains 30 to 40 aircraft". The number of strikes sharply increased under his watch, too: 53 in 2009, 117 in 2010, and 49 by the time Gregory delivered his lecture on September 26.

"CIA lawyers scrutinize the dossier for each target," he noted, adding that these documents normally stretch from two to five pages. "I'm told it takes 10 pages to get permission to run a wiretap in the United States. To kill somebody—two to five."

The attacks have also widened, he said, beyond al-Qaeda, beyond the Taliban, and extending to those linked to the Taliban, such as drug traffickers.

"The target lists have been extended beyond named individuals to people whose names the CIA doesn't know," Gregory maintained. "They've been identified on the basis of the systematic surveillance from the drones. The video feeds have been analyzed and analysts have decided that the pattern of life that they see...in those places, is a departure from the normal. These are the so-called signature targets."

He mentioned that since 2008, there have been estimates that the CIA killed 12 times as many low-level fighters than high-value targets with drone attacks.

Because the program comes under the CIA, the civilian staff who operate the drones remotely and fire missiles are not answerable to the Uniform Code of Military Justice, which regulates combatants.

Gregory pointed out that these people who work at CIA headquarters in Langley, Virginia have been characterized as "unlawful combatants" by Notre Dame law professor Mary Ellen O'Connell. This is the term Bush used to justify imprisoning Afghan warriors in Guantanamo Bay and hold them without charges for several years.

"But matters are not so straightforward," Gregory quickly added. "It turns out the U.S. Air Force has loaned predator and reaper drones to the CIA to give the agency more firepower [and] that the air force monitors the flights in and out of Pakistan."

Meanwhile, Obama has appointed a former senior military commander, David Petraeus, as head of the CIA. And the former head of the CIA, Leon Panetta, has become secretary of defense. Gregory likened this to a game of "musical chairs", blurring the lines between civilian and military operations.

The CIA has maintained that these strikes are exceptionally precise, minimizing civilian casualties. Gregory cited one report of a CIA drone firing a volley of missiles at a pickup truck carrying nine militants in a desolate area of Pakistan near the border with Afghanistan.

According to the CIA, no civilians were killed. But Gregory pointed out that a different version from the Bureau of Investigative Journalism reported that the missiles struck a religious school, an adjoining restaurant, and a house, killing 18 people—a dozen militants and six civilians.

"It's only courageous journalists on the ground and investigative journalists elsewhere that bother to count the numbers," he said.

Obama is a Harvard law graduate and used to teach constitutional law. One of his promises before taking office was that he would close the Guantanamo Bay detention facility and end the transfer of unlawful combatants to so-called "black sites"—locations in other countries where detainees were subject to waterboarding and other techniques tantamount to torture.

Now, he has nowhere to take these people apart from kidnapping them, putting them on trial in the United States, and having them sentenced to federal prison terms. So his administration is using civilians operating computers on U.S. soil to kill them with unmanned aerial vehicles in other countries.

Obama has something called "command responsibility". This holds him legally culpable for human-rights abuses committed by subordinates if he knew about them and failed to prevent them.

Expect to hear a lot more about that term in the coming years—particularly if the number of drone strikes continues to increase.

If you think travelling abroad has gotten legally troublesome for Bush, just wait until Obama leaves office.

Follow Charlie Smith on Twitter at twitter.com/csmithstraight.