A U.S. intelligence community whistleblower has leaked a trove of documents exposing the inner workings of President Barack Obama's global targeted drone assassination program. The documents, provided to The Intercept, show that in a single five-month period of U.S. drone strikes conducted in Afghanistan, nearly 90 percent of the people killed were unintended targets. Such killings in Yemen and Somalia are thought to be worse.

"From his first days as commander in chief, the drone has been President Barack Obama's weapon of choice, used by the military and the CIA to hunt down and kill the people his administration has deemed - through secretive processes, without indictment or trial - worthy of execution," writes The Intercept's Jeremy Scahill.

Despite the administration's insistence that remotely operated drone killings are precise operations, the near 10 percent success rate in that five-month period suggest otherwise and is among the most damning revelations to surface thus far regarding the CIA and Joint Special Operations Command drone programs.

The Intercept reveals in "The Drone Papers" report that drone attacks are often conducted after receiving unreliable intelligence gathered from electronic communications data, or "signals intelligence."

From The Intercept: "The source underscored the unreliability of metadata, most often from phone and computer communications intercepts. These sources of information, identified by so-called selectors such as a phone number or email address, are the primary tools used by the military to find, fix, and finish its targets. 'It requires an enormous amount of faith in the technology that you're using,' the source said. 'There's countless instances where I've come across intelligence that was faulty.' This, he said, is a primary factor in the killing of civilians. 'It's stunning the number of instances when selectors are misattributed to certain people. And it isn't until several months or years later that you all of a sudden realize that the entire time you thought you were going after this really hot target, you wind up realizing it was his mother's phone the whole time.'"

Officials acknowledge that such intelligence is insufficient, yet the program has continuously operated since 2001.

The report shows that when unintended people were killed by drones, they were subsequently categorized as "enemies killed in action" so that the administration could hide the true number of civilian casualties. The victims were sometimes family members or associates of actual targets, or often times just happened to have been nearby and mistakenly targeted.

It also highlights an instance when a British citizen was killed in a drone strike despite repeated opportunities to capture him instead, notes Wired.

At one point in 2012, Obama had approved 20 people for assassination in Yemen in Somalia, and 200 people ended up being killed in those countries that year, according to the Bureau of Investigative Journalism.

Since 2004, as many as 1,199 innocent civilians, including hundreds of children, have been killed by the U.S. drone program, the bureau notes.

"This outrageous explosion of watchlisting - of monitoring people and racking and stacking them on lists, assigning them numbers, assigning them 'baseball cards,' assigning them death sentences without notice, on a worldwide battlefield - it was, from the very first instance, wrong," writes Scahill.

One of the documents, marked as top secret, shows what the terrorism geolocation watchlist looks like on the computer screen of U.S. military personnel responsible for conducting drone operations. Next to the names of targets are unique codes associated with cellphone SIM cards linked to the individuals so they can be geolocated.

The documents were published by the website operated by Glenn Greenwald, the same man that former government contractor Edward Snowden leaked classified documents to in 2013 about U.S. surveillance programs. Snowden remains in exile in Russia out of fear that he would not receive a fair trial upon returning to the U.S.

"In an astonishing act of civil courage, one American just shattered an unspeakable lie," Snowden wrote on Twitter. "When we look back on today, we will find the most important national security story of the year. Today, @DanielEllsberg is smiling."

The FBI suspects that "an employee of a federal contracting firm" was behind the leaks and recently conducted a search on a suspect's home in Virginia, according to Yahoo!