Two of every three suspected crime guns recovered by Mexican authorities and reported to the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives came from the U.S., according to data the agency released Thursday.

The agency has come under intense criticism for an unsuccessful operation called Fast and Furious, which allowed suspected gun traffickers in Arizona to buy about 2,000 firearms without being immediately apprehended.

Originally designed as a probe to find high-level traffickers, the operation instead led to many guns being smuggled into Mexico that later turned up at crime scenes there and in the U.S. One was used in a 2010 shootout between federal agents and smugglers in southern Arizona that killed a U.S. border agent.

Attorney General Eric Holder has condemned the gun-walking tactic, but denied knowing about it until well after the fact. Congressional Republicans have blamed him for the botched operation.

The data released Thursday by the agency found that of the nearly 100,000 guns recovered by Mexico in the past five years and reported to U.S. authorities for tracing, more than 68,000 were either manufactured in the U.S. or legally imported to the U.S. before going to Mexico. The agency was unable to identify the U.S. source or trace the country of origin for the rest of the guns.