By Arianna Huffington at Huffington Post.

On March 17, 2011, four Hellfire missiles, fired from a U.S. drone, slammed into a bus depot in the town of Datta Khel in Pakistan's Waziristan border region. An estimated 42 peoplewere killed. It was just another day in America's so-called war on terror. To most Americans the strike was likely only a one-line blip on the evening news, if they even heard about it at all.

But what really happened that day? Who were those 42 people who were killed, and what were they doing? And what effect did the strike have? Did it make us safer? These are the questions raised, and answered, in a must-watch new video just released by Robert Greenwald's Brave New Foundation.

The attack was what has come to be called a "signature strike." This is when the CIA or the military makes the decision to fire based not on who the targets are but on whether they are exhibiting suspicious patterns of behavior thought to be "signatures" of terrorists (as seen on video from the drone). Given that the CIA is killing people it's never identified based on their behavior, one would assume a certain rigor has gone into defining the criteria for the kinds of behavior that get one killed.

So what's a signature behavior? "The definition is a male between the ages of 20 and 40," former ambassador to Pakistan Cameron Munter told the Daily Beast's Tara McKelvey. "My feeling is one man's combatant is another man's -- well, a chump who went to a meeting." The New York Times quoted a senior State Department official as saying that when the CIA sees "three guys doing jumping jacks," the agency thinks it is a terrorist training camp.

That day in Datta Khel, the signature behavior was a meeting, or "jirga," which is an assembly of tribal elders who convene to settle a local dispute. In this case, a conflict over a chromite mine was being resolved. And, in fact, the elders had informed the Pakistani army about the meeting 10 days in advance. "So this was an open, public event that pretty much everyone in the community and surrounding area knew about," says Stanford law professor James Cavallaro in the video.

Pretty much everyone in the community and surrounding area. But not U.S. intelligence. Or the head of the CIA. Or the president. Or the guy in Virginia or Nevada or some other undisclosed location pressing the button on the drone controller.

And so, almost all the tribal elders of the area were killed by the drone missiles. Akbar Ahmed is a retired Pakistani ambassador to the UK and now a professor at American University. "It's feeding into the sense that no one is safe, nowhere is safe, nothing is safe," he says in the video. "Even a jirga, the most cherished, the most treasured institution of the tribal areas. So we cannot even sit down and resolve an issue -- that is not safe anymore." As professor Cavallaro put it, "the loss of 40 leaders on a single day is devastating for that community."

And far from building stability in places like Pakistan, something the administration talks a lot about, in fact the strike actually removed, in one fell swoop, the most stabilizing forces in an entire community.

Jalal Manzar Khail was at his nearby home that day and remembers the attack, which also claimed four of his cousins. Khail's six-year-old son was later afraid -- not unreasonably -- to sleep in their house. "We cannot go home," Khail recounts his son saying. "We have to spend the night in the tree." Khail adds, "Convey my message to Americans: The CIA and America have to stop ... they're just creating more enemies and this will last for hundreds of years."

Khail's message is not uncommon. "At the end of almost every interview I did," Greenwald told me, "the person would say, 'Please tell President Obama I am not a terrorist and he should stop killing my family.'"

There was a time when President Obama might have been more receptive to that message. In the book Kill or Capture: The War on Terror and the Soul of the Obama Presidency, Daniel Klaidman recounts another drone strike just days after President Obama had been inaugurated. Among those killed were a pro-government tribal elder and two of his children. Obama "was not a happy man," an official told Klaidman.

The concept of the signature strike was then explained to him. "Mr. President," said CIA deputy director Steve Kappes, "we can see that there are a lot of military-age males down there, men associated with terrorist activity, but we don't always know who they are." Obama responded, "That's not good enough for me."

It would appear that he has since warmed to the concept. It's unknown how many have died -- combatants or civilians -- in signature strikes, since the administration still doesn't acknowledge that they happen. In February, Robert Gibbs told MSNBC's Chris Hayes that when Gibbs became Obama's press secretary he was told not to acknowledge the drone program at all. "You're not even to discuss that it exists," Gibbs remembers being told.

Of course, since then, given how increasingly ludicrous -- and insulting to the country -- this stance appeared, the administration has acknowledged the drone strikes, though not much more. But estimated numbers have been compiled by other sources. As Klaidmanpoints out, by the time Obama accepted his Nobel Peace Prize 11 months into his presidency, he'd already ordered more drone strikes than George W. Bush had in his entire presidency. By the end of 2012, he'd ordered six times as many strikes in Pakistan as Bush had. One study, conducted by professors from Stanford (including Cavallaro) and NYU, found that from 2004 to 2012, between 474 and 881 civilians were killed in Pakistan drone strikes. This includes 176 children -- the subject of another Greenwald video, which I encourage you to watch. For fiscal year 2013, the administration has requested $26.16 billion for the drone program -- at least that's the portion that we know about.

In a speech in May at the National Defense University, President Obama gave what was billed as a major national security address meant to clarify his policy on drones, surveillance, and Guantanamo. It seemed to signal a transition in his approach. "With a decade of experience to draw from," he said in the hour-long address, "now is the time to ask ourselves hard questions -- about the nature of today's threats, and how we should confront them." In parts of the speech he even made a good case against the use of drones:

... force alone cannot make us safe. We cannot use force everywhere that a radical ideology takes root; and in the absence of a strategy that reduces the well-spring of extremism, a perpetual war -- through drones or Special Forces or troop deployments -- will prove self-defeating, and alter our country in troubling ways.

He also admitted that "U.S. strikes have resulted in civilian casualties." This was a far cry from the claim made in 2011 by John Brennan, at the time the president's chief counterterrorism advisor, that "there hasn't been a single collateral death" from the strikes. He later amended this to say there's been no "credible evidence of collateral deaths." This ridiculous claim was demolished in an article in Foreign Policy by Micah Zenko, who concluded that Brennan either doesn't get the same briefings given to other administration officials or he doesn't have Internet access. Or "he was lying." In any case, it didn't stop his confirmation as director of the CIA.

In his speech, President Obama also allowed that "America cannot take strikes wherever we choose -- our actions are bound by consultations with partners, and respect for state sovereignty." Pakistan might differ on that one. After the Datta Khel strike, some of the victims' families filed suit, resulting in a ruling by the Pakistan court that the strikes are illegal.

In fact, the president opened his speech by proclaiming that "our alliances are strong, and so is our standing in the world." Well, the world's a big place. And there are some places where our standing has larger implications for our national security than others. In Pakistan, for instance, according to a recent Pew Foundation poll, 74 percent consider the U.S. to be an enemy. In the last year of the Bush administration, the U.S. was regarded favorably by 19 percent of the Pakistan people. By 2012, that had fallen to 12 percent. Bruce Riedel, a former CIA official and now a scholar at Brookings, says the strikes are "deadly to any hope of reversing the downward slide in ties with the fastest growing nuclear weapons state in the world."

The president also claimed that "conventional airpower or missiles are far less precise than drones, and likely to cause more civilian casualties and local outrage." Wrong again. In theGuardian last week, Spencer Ackerman reports on a study by Larry Lewis, of the Center for Naval Analysis, that found that drones strikes in Afghanistan were 10 times more likely to cause civilian casualties than strikes from manned fighters. "Drones aren't magically better at avoiding civilians than fighter jets," said study co-author Sarah Holewinski. "When pilots flying jets were given clear directives and training on civilian protection, they were able to lower civilian casualty rates."

In his speech, President Obama also said that "we must make decisions based not on fear, but hard-earned wisdom." The hard-earned wisdom the drone study was based on -- data in Afghanistan from 2010 to 2011 -- was presumably available to the administration. Had the White House been interested in finding out which method was safer, they could have. But they chose not to and instead just repeated the self-serving, conventional -- and demonstrably wrong -- "wisdom." It's hard to grant the mantle of actual wisdom to that kind of decision-making.

But the president also said that he was going to explore "other options for increased oversight," and that he'd signed "clear guidelines" for "oversight and accountability" just the day before. "Before any strike is taken," he declared, "there must be near-certainty that no civilians will be killed or injured -- the highest standard we can set."

Though signature strikes were not mentioned, some assumed language like "near certainty" and "highest standard" meant they were no longer going to be used. That assumption was proven wrong as just days later an administration official told the New York Times that signature strikes will continue in Pakistan, a statement the Times' Andrew Rosenthal wrote"seem[ed] to contradict the entire tenor of Mr. Obama's speech."

Two weeks later, on June 9, a drone struck a vehicle in Yemen, killing not only several supposed militants, but also a boy named Abdulaziz. He was 10 years old. "Near certainty" and those new "clear guidelines" apparently weren't enough for Abdulaziz. The administration refused to comment on the boy's death, or the strike itself. So much for accountability and transparency. And just last week, a strike in Waziristan killed 16 people and wounded five others.

In addition to asking some of those "hard questions" about the war on terror, it's time to start admitting some clearly obvious hard truths. And one of those is that the assumption that drone strikes make us safer -- even when they're on target and used with a threshold of absolute certainty -- just isn't true. So, it's not a choice, as the administration would have us believe, between safety and compassion. "As Commander-in-Chief, I must weigh these heartbreaking tragedies against the alternatives," said Obama in his speech. "To do nothing in the face of terrorist networks would invite far more civilian casualties." As if those are our only choices -- killing boys like Abdulaziz or doing nothing.

The president continued: "Let us remember that the terrorists we are after target civilians, and the death toll from their acts of terrorism against Muslims dwarfs any estimate of civilian casualties from drone strikes."

But he says that as if "the terrorists" are some set pool of people, and all we have to do is find them and kill them. Yes, given that terrorists target civilians, how about policies that don't create more terrorists in the first place? After that strike in Datta Khel, what do you suppose happened to the support of any moderate or pro-American or pro-democracy leaders in the community? (I'm speaking of the ones who weren't killed, of course.) Was their standing enhanced? Did the strike help them make their case?

Sure, we killed some people. Some of them were undoubtedly "bad guys" -- but has this made us safer? In the video, Lawrence Wilkerson, former chief of staff to Secretary of State Colin Powell, says it's not about casualty numbers. "The Vietnam body count as a metric was flawed," he says, "and the drone strikes are the same way ... Tell me how we are winning if every time we kill one, we create 10? That's not a metric that tells you if you're winning. What tells you if you're winning is if Muslims decide not to support the radical fringe." David Kilcullen, former senior advisor to General David Petraeus, agrees: "[T]he blowback and the aspect of political destabilization -- those things ultimately do make us less safe."

It seems clear that the White House doesn't want debate on this issue any more than it welcomed debate, as the president claimed, on the NSA's surveillance program after the Snowden revelations. What the administration seems to want is to make speeches in which they claim good intentions, high standards, and a commitment to transparency -- and then declare everything else classified and off-limits.

That's why Greenwald's new video is so valuable. It gives us a glimpse, even if the White House won't, of what's being done in our name. "We are working," Greenwald told me, "to use the video to get Congress to introduce legislation to ban signature strikes." So watch it, and then start the debate the president claims to want. The missiles from the drones might be exploding in Pakistan and Afghanistan and Yemen, but the fallout will impact us here at home for years to come.