ROSARITO, Mexico -- Saturday's ambush attack in broad daylight that left Rosarito's police chief Carlos Bowser-Miret dead has prompted U.S. officials to warn travelers to Mexico to be on alert.

According to Mexican authorities, two heavily armed gunmen opened fire spraying Bowser-Miret's car with more than 100 bullets.

Rosarito is 12 miles south of the U.S. border.

Several other assassinations have taken place in Mexico this year.

A memo from the U.S. Justice Department says Mexican commandos, trained by the U.S. military to help fight the drug cartels have switched sides -- and are now working for the cartels. They're known as "Los Zetas." One group was trained by the U.S Army at Fort Benning, Georgia.

Officials said the commandos are extremely violent and are blamed for a recent outbreak of violence along the Mexican border.

Despite recent violence south of the border, many of the people NBC 7/39 talked to Sunday said they were not concerned about their safety.

One-by-one, tourists lined up to cross the border, many of them from around the globe.

"We are from Germany, and we visited the United States and wanted to go to Mexico to by some cigarettes and (be able to say) we have been to Mexico," Ingolf, from Germany said.

Many American tourists also say they aren't concerned for their safety.

"I went twice. I went over to the clubs so it wasn't a problem. They had a lot of police out so I feel safe," Natalie Kelly said.

"I live in L.A. so I drive through downtown every day," Susy Custer said laughing. "I'm not really scared of that kind of thing anymore."

Experts said brutal attacks like the one Saturday are no laughing matter. They say people traveling to Mexico should be on the alert.

Saturday's Report

Bowser-Miret was gunned down Saturday morning when his unmarked police vehicle was leaving his home.

Immediately following the shooting officers did a sweep of the area.

Six suspects were taken into custody and three cars were confiscated, police said.

Police found rifles, pistols and masks inside the vehicles. Investigators said ballistic tests would be performed to see if the weapons matched those used in the killing.

At least three people, including a federal police officer, were killed in a separate shooting on Saturday in Reynosa, across the Texas-Mexico border.