SEATTLE AND MEXICO CITY — Lawmakers in Mexico are demanding an investigation into a U.S. law enforcement operation that allowed hundreds of weapons to flow into the hands of Mexican drug cartels amid claims from a ranking legislator that at least 150 Mexicans have been killed or wounded by guns trafficked by smugglers under the watch of U.S. agents.
U.S. authorities say manpower shortages and the high number of weapons sold resulted in their losing track of hundreds of guns, from pistols to .50-caliber sniper rifles, though a federal agent deeply involved in the Phoenix-based operation said it was "impossible" that U.S. authorities did not know the weapons were headed for Mexico.
The Bureau of Alcohol, Tobacco, Firearms and Explosives has acknowledged that at least 195 weapons sold in Arizona under Operation Fast and Furious have been recovered in Mexico, traced as a matter of routine via serial numbers after their recovery from crime scenes, arrests and searches.
The Mexican lawmaker did not say how the new casualty statistics were calculated. But the estimates, which could not be independently confirmed, provide troubling new fallout from an investigation in which guns sold to suspected smugglers in the U.S. already have been linked to the deaths of two U.S. law enforcement agents.
Humberto Benitez Trevino, a federal deputy who chairs the justice committee in the lower chamber of Congress, the Chamber of Deputies, said in comments released by Congress this week that "we have 150 cases of injuries and homicides with arms that were smuggled and passed illegally into our country."
Benitez said the figure came from "sources," but he did not specify who the victims were or where shootings took place.
"This was an undercover program that wasn't properly controlled," Benitez said.
A U.S. law enforcement official on the border, who is a defender of the ATF program, said he didn't know how Mexican officials came up with the casualty figure. "It's probably just a good political thing to say, and how are you going to refute it?"
Nevertheless, the new information is bound to complicate U.S.-Mexico relations at a rocky time. Mexican President Felipe Calderon is already upset at U.S. Ambassador Carlos Pascual over a series of leaked diplomatic cables citing shortcomings in Mexico's 4-year-old war against drug cartels.
Mexican politicians have criticized the ATF program as a violation of Mexico's sovereignty and evidence of U.S. arrogance toward its southern neighbor.
Lawmakers from all of Mexico's main political parties have demanded to know whether Mexican authorities were aware of the program.
"This is a serious violation of international law," said lawmaker Carlos Ramirez Marin, a member of the opposition Institutional Revolutionary Party and president of the Chamber of Deputies. "What happens if next time they need to introduce trained assassins or nuclear weapons?"
The new claims came amid growing demands for an independent investigation in the U.S.
In Washington, Senate investigators are trying to determine whether the gun used in the attack that killed Immigration and Customs Enforcement agent Jaime Zapata in February -- purchased at a Texas gun store in October -- was smuggled into Mexico by buyers who were under investigation by ATF agents.
U.S. Sen. Charles E. Grassley (R-Iowa), ranking member of the Senate Judiciary Committee, has asked the ATF why the purchasers of the gun used in the attack on Zapata were not arrested in November, a month after they bought the weapon.
"After the delivery of the illegal weapons, the three men were stopped by local police. Why were these traffickers not thereafter arrested in November?" Grassley said in a letter to the agency, which asked whether the gun made its way into Mexico after this initial contact with law enforcement agents.
"Naturally, this raises questions about whether the ATF strategy of allowing [smugglers] to continue to operate in hopes of making bigger cases may have contributed to the shooting of ICE Agent Jaime Zapata."
Thomas Crowley, ATF spokesman in Dallas, said it was not known when the gun was transferred to Mexico.
But John Dodson, an ATF agent in Phoenix who worked on the Fast and Furious effort and became alarmed enough to alert Senate investigators, said in an interview that the number of guns sold to known traffickers under the eyes of the ATF was so large that it was "impossible" the agency didn't know the weapons were going to Mexico.
"The day I started, there were 240 guns they had let ... out of Fast and Furious," he said. "Guns they were purchasing were showing up on both sides of the border already."
"I mean, ... a guy comes in and purchases 10 AK-47s, and four of them he purchased last time have already shown up on the other side of the border? And you keep going?" Dodson said.