(With permission from the Investigative Reporting Workshop.)

Armed with assault rifles and hand grenades, Arturo Beltran Leyva, head of one of the most ruthless drug cartels in Mexico, battled hundreds of Mexican navy commandos with six of his bodyguards from a luxury high-rise Cuernavaca apartment in December 2009. Two hours later, Beltran Leyva and his men lay dead amid the heavy stench of gunpowder, pools of blood and puddles of water from pipes pierced by gunfire. A grenade killed one commando and wounded six others, and a passerby died from a gunshot wound.

At the time, the takedown of Beltran Leyva was heralded as the high point of Mexican President Felipe Calderon’s war against the cartels and as evidence of growing U.S.-Mexico bilateral effectiveness. In a classified cable from the U.S. Embassy in Mexico City, and recently disclosed by WikiLeaks, officials hailed the military operation as “one of the greatest successes to date in the counternarcotics fight.”

Not mentioned in the celebratory cable, however, was that during the weeklong chase and takedown of Beltran Leyva, Mexican authorities seized a wartime cache of weapons, grenades, scopes, silencers and nearly 9,000 rounds of ammunition. Many of the guns recovered in the operation would later be traced back to the United States. More alarming, nearly half of the 62 rifles seized were Romanian AK-47s that had come from a single gun shop, X Caliber, in the north suburbs of Phoenix.

Read full story at the Investigative Reporting Workshop…

*Young is a producer for FRONTLINE/Investigative Reporting Workshop. Cummings is reporter for the Investigative Reporting Workshop and a contributing writer at InSight.

Other Stories in the Series:

GunRunners: Introduction to the Joint Project

How Guns are Trafficked Below the Border

How the Beltran Leyva, Sinaloa Cartel Feud Bloodied Mexico

The Takedown of the ‘Boss of Bosses’

CPI: Romanian Weapons Modified in the U.S. Become Scourge of Mexican Drug War