Editor’s Note: As drugs and violence flow north from Mexico, guns are heading south from the U.S. Our Ed Lavandera rides along with an ATF agent for part one of the American Morning original series “The Gun Trail.” Tomorrow, he heads to Savannah, Georgia to see how gun smugglers are taking advantage of the state's weaker gun laws, and why shop owners say they're not part of the problem.
[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/02/15/guns.sign.mx.gi.art.jpg caption="A sign warning border-crossers that weapons are forbidden in Mexico is posted on the streets of the border town of Lukeville, Arizona."]
By Ed Lavandera, CNN
We drove the streets of Houston with an agent from the Bureau of Alcohol, Tobacco and Firearms (ATF). We can't tell you who he is because he's in the midst of the biggest case he's ever worked; battling lethal Mexican drug cartels on American streets.
"We started seeing [the guns] popping up in Mexico and then further down in Guatemala is where it really opened our eyes that we're onto something pretty big here," the agent says.
What they found was a trail from Houston to Guatemala littered with almost 340 guns purchased by so-called "straw buyers” – 23 Houston-area residents, all with squeaky clean records and legally allowed to buy guns.
Investigators say almost 100 of those guns have since turned up at crime scenes south of the border, in the hands of the drug cartels.
Watch "The Gun Trail" part one 
"They're fighting each other for turf in Mexico. And unfortunately, many law enforcement and civilians are being killed in that fight," says Special Agent in Charge Dewey Webb.
Investigators say John Phillip Hernandez, a regular guy in his mid-20s, was at the center of the elaborate straw-purchasing scheme.
According to ATF investigators, Hernandez recruited a crew of 23 people to purchase firearms for the drug cartels at gun shops across Houston.
Court documents show Hernandez bought six weapons and ammunition at a Houston gun shop and one of those weapons was later connected to the kidnapping and murder of a Mexican businessman.
Hernandez also admitted to buying weapons used in the infamous 2007 “Acapulco massacre," where seven people, including four police officers, were slaughtered by a dozen armed drug traffickers.
According to court documents, Hernandez purchased four weapons at one shop where the owner told us Hernandez then returned a few weeks later flashing $20,000 in cash and wanting to buy 20 more weapons. The owner says he rejected the sale.
Investigators say the cartels paid Hernandez $100 to $200 each time they bought a firearm.
"People that are buying drugs in the United States have just as much blood on their hands as the people pulling the trigger in Mexico," says Agent Webb.
John Phillip Hernandez is now serving an eight year prison sentence after pleading guilty. But this ATF agent says as one ring is broken up, new rings can quickly emerge on Houston's streets, on the gun trail from America to Mexico.