On July 23, another US Border Patrol agent lost his life in the line of duty.

According to press reports, Agent Robert Rosas, 30, the father of two, was shot in the head and body when he responded to a border incursion near the isolated town of Campo in southeastern San Diego County. He was dead when other agents arrived, Keith Slotter, special agent in charge of the FBI's San Diego bureau, told the Associated Press.

This morning, Mexican authorities named Ernesto Parra Valenzuela, 36, as the shooter in the case. He was arrested by Mexican police in the town of Tecate on Friday, in possession of a US Border Patrol pistol. Four other men were arrested with him and Jose Eugenio Quintero Ruiz, 49, a coyote, identified Valenzuela as the killer.

Last year, on Jan. 19, Border Patrol Agent Luis Aguilar was also killed in the line of duty when he was struck by a car fleeing into Mexico. The accused killer was Jesus Navarro Montes, a 22-year-old who was arrested for unrelated charges of border smuggling and human trafficking. Montes was picked in the Mexican town of El Yaqui three days after the killing and charged with Aguilar’s murder.

At that time, however, Mexican federal Judge Laura Serrano set Montes free on bail and he disappeared. When US authorities, including then-Homeland Security Secretary Michael Chertoff protested, Mexican officials claimed that US prosecutors never requested extradition.

“No arrest warrant was presented, no evidence was offered and no one from the US government contacted Mexican authorities concerning his extradition. We couldn’t hold him with no evidence of a crime. We needed help, but we never got it.” Ricardo Alday, spokesman for the Mexican embassy, told reporters in July, 2008, according to the article. “The Life and Death of Luis Aguilar " in the September 2008 issue of Homeland Security Today.

At the time, Chertoff and US officials vowed that they would launch a “relentless pursuit of justice” and pursue Montes. However, new charges were never filed.

Last Friday, Homeland Security Secretary Janet Napolitano announced that: "This act of violence will not stand—nor will any act of violence against the Border Patrol. I have directed that the full resources of the Department assist in the investigation to find and bring to justice those responsible for this inexcusable crime."

Much has changed in Mexico and on the border since the murder of Luis Aguilar. We shall see the degree of that change--and whether it has been effective--as we follow the arrest, extradition (we presume) and trial of Ernesto Valenzuela. This will be an important test of both the government of Mexican President Felipe Calderon and his crackdown on crime and Secretary Janet Napolitano's new Department of Homeland Security.