The testimony of a Mexican hitman turned government witness has revealed some astonishing details of life inside Mexico's criminal underworld. Most astonishing of all: claims that cartel assassins obtained guns from the U.S. Border Patrol.

According to Mexican magazine Revista Contralinea, the testimony comes from a protected government witness and former hitman, who cooperated in the prosecution of a Sinaloa Cartel accountant by the Mexican Attorney General’s Office. The testimony details a series of battles fought by a group of cartel members attempting to drive out rival gangsters from territory in Mexico’s desert west. To do it, the group sought weapons from the U.S., including at least 30 WASR-10 rifles — a variant of the AK-47 — allegedly acquired from Border Patrol agents.

If true, it could reignite the debate over Operation Fast and Furious, the last time U.S. authorities allowed guns to fall into the hands of Mexican gangsters. Two days after the election, Attorney General Eric Holder – who had been at the center of allegations surrounding the scandal – is now talking like he might not stay with the administration for much longer. "That's something I'm in the process now of trying to determine," Holder said Thursday. "I have to think about, can I contribute in a second term?"

Though we don't know if the informant, who goes by the pseudonym "Victoria," is telling the truth about gangsters getting guns from the Border Patrol. (A spokesperson for the U.S. Customs and Border Protection, which oversees the Border Patrol, tells Danger Room that the agency is checking on the claim.)

The witness named "Victoria" first joined a Sinaloa Cartel enforcer group called Gente Nueva, or New People, in 2009. Within Gente Nueva, the witness worked for smaller group called the Javelins. Their job, over 2009 and 2010, was to eliminate groups of rival Zetas and Beltran Leyva Organization members that had seized Sinaloa Cartel turf in Mexico's desert west. The enforcers moved by convoy, ranging from 20 to 80 trucks and SUVs with five or six gunmen in each, and fought a series of pitched battles over control of the area's "plazas," or hubs for moving cocaine and marijuana.

"The instruction was to kill them all," the witness said.

In July 2010, gun battles erupted a few hours south of the Arizona border near the towns of El Saric and Tubutama. "We moved in 20 trucks with five gunmen in each, trying to enter the town of Zaric [sic] – four hours distant from Nogales – at five in the morning to find homes where there were Los Zetas," the witness said. "But we were ambushed and sparked a confrontation that lasted two hours."

The fighting was remote and sparsely reported. Los Angeles Times reporter Richard Marosi was one of the few to make it in, and described the fighting in the area as a "siege of medieval proportions that has cut off a region about the size of Rhode Island." Beltran Leyva fighters, isolated in small towns by patrolling Sinaloa Cartel convoys, were literally being starved out. Some of the fighting was estimated to include more than 100 gunmen on a side, or around the size of a U.S. infantry company. During fighting in the border city of Nogales the previous year – across the border from the Arizona city of the same name – gunmen took to marking their vehicles "with an X in the body to distinguish the opposing side."

At one point, the witness was ordered to help dig up and rebury two police officers killed for assisting a rival cartel. In December 2009, the group set out in an 80-vehicle convoy to patrol Nogales. Trucks scattered and the group fought "several clashes in different places" over a period of three days, and executed several captured Zetas. Another patrol elsewhere in the state had to be called off after authorities mobilized and set up checkpoints on the roads.

The Javelins' leader, Jose Vazquez or "Wild Boar" also seems to have been in charge of a pretty sophisticated operation. The group fielded escort teams for carrying weapons shipments and controlling drug trafficking routes, and teams of 12 for smuggling marijuana across the border. Cocaine was flown in from southern Mexico before being smuggled. They even had one command-and-control station for monitoring cameras placed along key highways.

Underneath Vazquez, according to the witness, was a deputy in Tucson in charge of smuggling weapons from the United States. Another deputy in Mexico was in charge of receiving the weapons. There was a deputy tasked with "cooptation of [Mexican] authorities" on the local, state and federal levels. Vazquez also had an accountant responsible for "organizing the logistics of fighting with other cartels," paying for weapons including those allegedly obtained from the Border Patrol, and managing salaries. (The witness had a salary of $6,000 per month.)

We don't know if the witness is telling the truth. And even if he or she is, we're still not sure who the cartel had on the inside or who within the Border Patrol was selling guns.