The United States, with nearly as many guns as people, has more than 100,000 licensed gun sellers, an industry that makes about 2.8 million small arms a year, and gun laws so loose that arms traffickers easily pick up any weapons they need.
Despite Mexico's gun-control laws, criminals have long smuggled guns in from the United States.
"The problem is getting bigger because the illegal possession of arms, and their clandestine introduction to our country, combines with narcotics trafficking," said a government report to Mexico's Senate in June.
It said 99.4 percent of the weapons in the hands of Mexican criminals are suspected of coming from the United States.
At least 11,752 US-sold guns have been found in Mexico since January 2003 -- a tiny fraction of what remains on the streets, according to the report.
Particularly worrisome are US sales of Belgian-made FN-57 pistols. These fire bullets that "will defeat most body armor in military service around the world today," according to the Remtek weapons site on the Internet. They sell for $800 to $1,000 each at dozens of gun stores within a day's drive of the border.
The weapons were unheard of in Mexico until they were used to kill at least a half-dozen police officers this year.
Among them were Mexico City policemen Felix Perez and Jose Rodriguez, slain in May when a car full of suspected mobsters fired FN-57s whose bullets sliced right through the officers' body armor.
