Gunmen shot and killed U.S. Border Patrol agent Robert Rosas in California near the U.S.-Mexico border fence on July 23, the first such fatal shooting in more than a decade. In rugged desert where people smugglers and drug traffickers roam, Rosas was tracking a suspicious group of people near the rural town of Campo, about 60 miles (97 kms) east of San Diego.

After radioing for backup, he got out of his vehicle and started to follow members of the group as it split up. He was attacked, robbed of his weapon and shot several times in the head and abdomen.

Mexican police have rounded up five suspects believed to be coyotes, or people smugglers, and drug gang members, although the FBI, which is heading the investigation, considers the case unsolved.

While it unfolds, the probe into the murder of 30 year-old Rosas, father of two small children and whose memorial service is on Friday, is a test for U.S.-Mexican cooperation. Both countries are at pains to show a unified alliance in the drug war, underscored again by U.S. drug czar Gil Kerlikowske’s visit to Mexico this week.

But Rosas’ murder is also a warning that Mexican organized crime is increasingly undaunted by U.S. law enforcement. In Mexico, well-armed drug cartels take on the army at will. Mexico’s escalating drug war has killed some 12,800 people since late 2006, when President Felipe Calderon launched his army-backed crackdown on cartels.

Attacks are also rising against the Border Patrol on the U.S.-Mexico border as drug gangs, pressured by increased enforcement and the border fence, link up with people smugglers to use illegal immigrants to smuggle narcotics across the border.

Border Patrol agents often work alone in remote stretches of the 2,000-mile (3,200-km) border and traffickers are willing to use brutal violence against them if threatened. Last year, Border Patrol agent Luis Aguilar was intentionally run over and killed by a smuggler in a drug-packed Hummer in Arizona.

According to U.S. security consultancy Stratfor: “such deaths in the United States can be considered almost inevitable, especially considering that authorities report nearly 50 Border Patrol agents were fired on during 2008.” In Tucson sector alone in the first 10 months of fiscal 2009 there have been 171 assaults on Border Patrol agents.

Disarming Mexican drug cartels, who have easy access to assault weapons in gun shops in U.S. border states, is one of the central strategies of the drug war but one that is making limited progress.