Monday’s arrest of three men in Texas for trafficking guns, one of which was apparently used in the attack which killed U.S. agent Jaime Zapata in mid-February, raises several key issues about the problem of gun trafficking at the Mexico border.

According to the U.S. Attorney’s Office for the Northern District of Texas, one of the three guns used in the attack that killed Zapata was originally purchased by Otilio Osorio on October 10, 2010, in Dallas. Osorio was already under investigation by federal authorities for alleged involvement in a gun trafficking ring, along with his brother Ranferi and their neighbor Kelvin Leon Morrison, also arrested Monday.

The investigation against the Osorio brothers began in November, when an informant for the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) met with them and asked for 40 guns to smuggle into Mexico, court documents say. The two Osorio brothers reportedly loaded the weapons, all with obliterated serial numbers, into the informant’s vehicle and drove to Laredo, where they were stopped and identified by local police. Morrison, who had accompanied them in the truck, was also detained.

It is unclear why the ATF waited to mobilize and get an arrest warrant for Osorio after the November incident. It is also unclear how the firearm purchased by Osorio in October, allegedly at a gun show, later turned up in the hands of the Zetas, who were responsible for the attack that killed Immigration and Customs Enforcement (ICE) agent Jaime Zapata on February 15.

But it already looks as though the Osorio case may become a textbook example of the havoc that U.S. “straw buyers” can indirectly cause in Mexico. As detailed by InSight’s joint GunRunners investigative project with PBS Frontline, the Investigative Reporting Workshop at American University and the Center for Public Integrity, middlemen buy high-power assault weapons in the U.S. from licensed stores or gun shows. They then move the weapons south where they may end up in the hands of characters like alias ‘El Piolin,‘ presented as the main suspect in Zapata’s death. 

The Osorio case also raises two key issues. The first is the need for legislation that would better allow ATF agents to track “straw buyers” who purchase a high number of assault weapons within a short period of time. Morrison, arrested Monday along with the Osorio brothers on gun trafficking charges, reportedly bought 24 weapons within a three-month period in 2010. If licensed gun shops did more to report suspicious sales of firearms, it could help the ATF to intercept more weapons before they head south, and build stronger cases against middlemen buyers for the Mexican cartels.

The second issue is the alarmingly short amount of time it took the gun allegedly purchased by Osorio to apparently end up in the hands of the Zetas in San Luis de Potosi. In terms of “time to crime” — the measurement that the ATF uses to track how soon a gun purchased legally in the U.S. ends up at a crime scene in Mexico — this is only about four months. This is a reminder that there are sophisticated and efficient arms trafficking networks at work in border states like Texas.

There are 3,800 gun retailers in Texas. The ATF’s Project Gunrunner program, which has a field office in Dallas, is supposed to monitor all of these dealerships for suspicious sales. But without the legislation needed to track bulk sales of assault weapons, the ATF is working with one hand tied behind its back. And it looks as though the “time to crime” figures aren’t getting any lower.