Reports: Sergio Salcido Luna killed

Violence at the U.S.-Mexico border crossing near Tijuana claimed the lives of two American citizens early Monday morning, including a young man with nine professional mixed martial arts bouts.

Sergio Salcido Luna, 25, a professional fighter since 2005, and 28-year-old Kevin Joel Romero -- co-workers at West Coast Beverage, a San Diego-based company that services draft beer equipment -- were shot dead with a 9 mm weapon as they waited in a company truck at the San Ysidro border crossing at around 2:40 a.m. PT, according to published reports.

The assailant approached on foot between the lines of vehicles, fired his weapon and fled, according to the San Diego Union-Tribune, which cited a Mexican law-enforcement source. Salcido and Romero were shot in the head, chest and arms.

After suggesting the shooting could be drug-related, the Baja California Attorney General's Office ruled out that possibility on Tuesday. Investigators first believed a small amount of marijuana was found on Salcido, but testing revealed the fighter was not in possession of illegal drugs, according to the Union-Tribune.

Neither Salcido nor Romero had a criminal record, according to a U.S. law-enforcement source who spoke to the Union-Tribune.

Matt Pelot, the owner of West Coast Beverage, told The Los Angeles Times that the men had moved to Mexico for family and financial reasons and were trying to avoid traffic by getting to the border crossing before 3 a.m. PT.

Salcido amassed a 4-5 record while competing at welterweight. His career began promisingly enough with four victories in his first five bouts, however he lost his last four since 2009. Salicido was in the midst of training for a fight in June, according to a report by NBCSanDiego.com.

Information from ESPN.com's Josh Gross was used in this report.