President Barack Obama handed over to lawmakers Friday a trove of documents related to Operation Fast and Furious, a failed federal gun trafficking investigation that allowed weapons to be smuggled into Mexico.  In an unusual move, the House of Representatives voted in 2012 to hold then-Attorney General Eric Holder in contempt after Obama asserted executive privilege to keep the documents out of the hand of lawmakers.

Now, with just months left in his administration, the president released the documents to Congress, according to Politico. Rep. Darrell Issa, R-Calif., former chairman of the House Committee on Oversight and Government Reform, and Sen. Chuck Grassley, R-Iowa, chairman of the Senate Judiciary Committee, have been leading investigations into “gunwalking” operations in which federal authorities let illegal straw buyers purchase arms in order to learn where the weapons wind up. The U.S. Department of Justice's Office of the Inspector General is also investigating the practice.

The backlash over the gunwalking operations led Obama to invoke executive privilege for the first time in his presidency to keep documents out of the hand of lawmakers.

Between 2006 and 2011, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives ran a number of gunwalking operations in Arizona that allowed illegal gun purchases with the aim of tracking the guns to Mexico and capturing drug cartel bosses. It was part of a larger program aimed at stemming the flow of firearms to Mexico, whose government has long complained about the flow of weapons from gun shops north of the border into the arms of murderous narco-hitmen.

The largest of the gunwalking operations was Operation Fast and Furious, named after the car-racing film franchise because the gun trafficking suspects the authorities were tracking belonged to a car club. The operation turned controversial after guns that ATF allowed to be sold ended up at crime scenes on both sides of the border, most notably one involving the murder of U.S. Border Patrol Agent Brian Terry in 2010.

Mexican lawmakers say some of these guns were found at crime scenes in which about 150 Mexican civilians were killed or wounded. Out of about 2,000 guns the ATF allowed to “walk,” only 710 were recovered. Though some low-level crooks were prosecuted, no high-level drug cartel operative was ever captured in the scheme.