A routine traffic stop by a state trooper in Denton County last week led to the seizure of 17 assault-type rifles, ammunition, body armor and 20 black ski masks, investigators said.
It all may have been headed to Mexico, federal agents said.
A Texas Department of Public Safety trooper stopped a car on Interstate 35 near Denton on Oct. 23 for not having a front license plate. The two men inside seemed "extremely nervous," according to court documents.
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The driver, Victor Manuel Villalpando, 28, of Burleson, ran into a wooded area and was arrested after a manhunt.
The passenger, Norberto Estrada, 24, of Fort Worth, was detained at the scene.
Both men were taken to the Denton County jail.
The weapons were found in a search of their car, and many of the serial numbers had been obliterated, according to the documents.
The men were already under investigation by the U.S. Bureau of Alcohol, Tobacco and Firearms for running guns to Mexico, an ATF agent wrote in the men's arrest warrant.
U.S. federal agents have focused on intercepting weapons shipments to Mexico, but it remains a problem along the Texas-Mexico border, ATF spokesman Tom Crowley said.
"The drugs come north, the guns go south, and those guns are fueling all the violence among the drug cartels," Crowley said.
More than 90 percent of the weapons recovered in Mexico come from the U.S., most of them from Texas, he said.
"It's just supply and demand," he said.
Read the official documents here: (PDF link)