Though the Mexican nationals were not charged with gun smuggling, officials say there is no doubt the weapons were being taken back across the border.

Those here illegally are prohibited from possessing a firearm as well as ammunition.

Recently, Sen. Chuck Grassley (R-IA) began investigating a claim that the bandits who gunned down U.S. Border Patrol Agent Brian Terry were armed with assault rifles purchased in a Glendale, Arizona, gun store and were actually allowed to be smuggled across the border as part of an ongoing sting investigation being carried out by the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Grassley says that he has information that the AK-47s found at the scene of Agent Terry’s murder were traced back to Project Gunrunner, a program aimed at stopping the illegal flow of guns to the drug cartels in Mexico.

Grassley wrote a letter to ATF Director Kenneth Melson, which reads: “Members of the Judiciary Committee have received numerous allegations that the ATF sanctioned the sale of hundreds of assault weapons to suspected straw purchasers, who then allegedly transported these weapons throughout the southwestern border area and into Mexico. According to the allegations, one of these individuals purchased three assault rifles with cash in Glendale, Ariz., on Jan. 16, 2010. Two of the weapons were then allegedly used in a firefight on Dec. 14, 2010, against Customs and Border Protection agents, killing CBP Agent Brian Terry.”