(CNN)  -- The alleged leader of a firearms trafficking network believed to be smuggling guns into Mexico -- where police say they are used against law enforcement officers by members of Mexican drug cartels -- was arrested Thursday in Arizona, authorities said.



Victor Varela was arrested by the ATF as part of the agency's ongoing Project Gunrunner.



Victor Varela was arrested by the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives as part of the agency's ongoing Project Gunrunner, according to an ATF release. He was in the custody of the Maricopa County, Arizona, sheriff.



"Law enforcement officers disrupted a group of gun traffickers and recovered several weapons, including .50-caliber semiautomatic rifles and several handguns, allegedly intended to supply drug traffic organization members of the Juarez Cartel in Palomas, Mexico," the statement said.



In state charges, prosecutors allege Varela and his co-defendants bought a number of guns in Arizona intending to supply the Mexican cartel members. The group allegedly transported the illegally purchased guns to New Mexico, and then into Mexico.



A .50-caliber weapon is the largest that can legally be bought in the United States, and is illegal in Mexico. Authorities believe a .50-caliber weapon was used in recent months to kill Francisco Ledesma Salazar, a police commander in Juarez, Mexico. He is among five high-ranking Mexican police officials killed this year in what Mexico authorities describe as an escalating war between police and drug cartels.



Last week, 2,000 troops were sent to Juarez by the Mexican government in an effort to quell the violence there, which has claimed some 200 lives since January.



Guns are difficult to buy legally in Mexico, but can be obtained just north of the border at gun shows and gun shops. Project Gunrunner was launched as an effort to help Mexican police by cracking down on illegal smuggling of guns and ammunition, and has led to several arrests and seizures.  Watch how the weapons fuel a little-known war »



"This case was made one of our highest priorities because of the nature of the crime alleged to be committed by Varela," U.S. Marshal David Gonzales said in the ATF release.



Guns featured in a CNN Special Investigations Unit report last week, confiscated by Juarez police, are believed to have been smuggled into Mexico by Varela, according to an ATF spokesman.



Authorities said one recent discovery, in a storage locker in Yuma, Arizona, yielded 42 weapons and hundreds of rounds of .50-caliber bullets already belted to be fed into a machine gun-style weapon, as well as Fabrique Nationale pistols, semiautomatic handguns that fire a 5.7-by-28-millimeter round.



"What's interesting about this gun, why it's in high demand, is the nickname that it has in Mexico," said William Newell, ATF special agent in charge, about the Fabrique National pistol. "It's called 'mata policias,' or 'cop killer.' "



Charging documents allege that Varela was attempting to buy a fully automatic M-60 machine gun for a drug cartel associate in Palomas, authorities said. "Additionally, a number of firearms recovered by Mexico law enforcement ... allegedly were trafficked by Varela's gun smuggling network," the ATF statement said.



U.S. authorities are sharing intelligence with their Mexican counterparts to assist in ongoing investigations, the ATF said. E-mail to a friend



CNN's John Murgatroyd and Drew Griffin contributed to this report.
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question: who is suspect?, answer: Victor Varela | question: who is blamed for killings of police officers?, answer: drug cartels. | question: how many troops were sent to juarez?, answer: 2,000 | question: How many Mexican troops were sent to Juarez,  Mexico?, answer: 2,000 | question: Who is blamed for the killings of police officers?, answer: drug cartels. | question: who is sharing intelligence, answer: U.S. authorities are | question: Who is sharing intelligence with their Mexican counterparts?, answer: U.S. authorities | question: where are the guns being smuggled, answer: Mexico