According to the Washington Post, the CIA has been closely involved for a decade in a secret fight against drug cartel FARC in Colombia, including by targeting and killing its top leaders.

In a long investigative feature published by the Post on Sunday, it's revealed that while public shows of support like the US's Plan Colombia aid package reveal close ties in the conflict against the FARC – a decades-long war that has cost the lives of at least 200,000 – the ties are even closer than ever imagined.

The collaboration between the U.S. and Colombia, the story reveals, really shifted in 2006, when the U.S. Air Force's mission chief arrived there and proposed smart bombs as an efficient, effective tool in the fight, like the ones used to kill Iraqi al-Qaeda chief Abu Musab al-Zarqawi. Because of their acknowledged "human rights problems," Colombia would propose a target and the United States would get a final sign-off on the act.

Some of the meatiest parts of the story tackle the interesting question of whether or not the program constituted an assassination, which would make it illegal. The writer, Dana Priest, explains how the US wrangled the law into letting this work: 

The White House’s Office of Legal Counsel and others finally decided that the same legal analysis they had applied to al-Qaeda could be applied to the FARC. Killing a FARC leader would not be an assassination because the organization posed an ongoing threat to Colombia. Also, none of the FARC commanders could be expected to surrender.

Later, when presented with an opportunity to kill FARC number-two Raul Reyes in Ecuador, lawyers had to figure out how to send a Colombian plane carrying U.S. weaponry into a foreign land. What they decided would have far-reaching legal consequences:

U.S. national security lawyers viewed the operation as an act of self-defense. In the wake of 9/11, they had come up with a new interpretation of the permissible use of force against non-state actors like al-Qaeda and the FARC. It went like this: If a terrorist group operated from a country that was unable or unwilling to stop it, then the country under attack — in this case, Colombia — had the right to defend itself with force, even if that meant crossing into another sovereign country.

This was the legal justification for CIA drone strikes and other lethal operations in Pakistan, Yemen, Somalia and, much later, for the raid into Pakistan that killed Osama bin Laden.

Reyes was killed in March 2008, but not without touching off the Andean diplomatic crisis, a firestorm that caused Venezuela and Ecuador to move troops to the border and prompted an eventual apology from Colombia.

Ever since the U.S. gave up the final sign-off to such bombings, in 2010, things have changed even more dramatically, the Post finds. In the three years before the CIA gave Colombia complete control of their smart-bomb technology, they had killed five top FARC leaders by airstrike. In the three years after, 35 top leaders have been reported killed this way. Many have fled, and FARC can no longer travel in large groups. Reports suggest popular support is dwindling.

"There was a great deal of excitement,” recalled William Scoggins, counternarcotics program manager at the U.S. military’s Southern Command. “We didn’t know the impact it would have, but we thought this was a game changer.”

The much-maligned NSA takes a bow as well, with Scoggins also referring to the agency's signal intercept ability as a game changer for these missions, suggesting he probably should have come up with different synonyms with which to show his enthusiasm.

Whether or not it's mere coincidence that FARC and the government of President Juan Manuel Santos – Colombia's defense minister during the hike in US involvement – appear to be making the most legitimate headway in negotiations since the 1999-2002 peace efforts remains to be seen. (The story quotes Santos as believing they're directly linked.) A week ago, FARC offered a Christmas-long ceasefire, which Santos rejected, before proceeding to wreak more havoc on the organization.

For whatever it's worth, FARC came to power in the mid-80s as a result of a power vacuum left by Colombia's crackdown on the major cartel at the time, Pablo Escobar's Medellin. So while the story offers much opportunity for back-patting about the major hits that FARC is taking, it is unclear whether or not this will produce lasting peace in a country long torn by strife.

Make this story your long-read du jour, as it's an incisive, access-heavy news feature that offers a revealing portrait of how a war is waged, and how doing it has changed in the high-tech, free-wheeling post-9/11 world.