Mexican and U.S. officials estimate the number of American weapons crossing the border in the thousands, the Los Angeles Times reported Sunday.

U.S. sources have been found in over 90 percent of guns seized at the border or after raids and shootings, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives says. In 2007 that meant some 2,455 weapons had been purchased in the United States, according to the ATF. The states of Texas, Arizona and California accounted for the vast majority of traced weapons.

More than 6,700 licensed gun dealers operate within a short drive of the border in those states. That equals more three dealers for every mile of border territory, with straw buyers often having little trouble purchasing weapons for Mexican usage, say officials.

"Just like the drugs that head north," firearms move south, said Tom Mangan, a senior ATF special agent in Arizona. "The cartels are outfitting an army."