WASHINGTON — The morning started like any other for the traveling jewelry salesman as he checked out of a motel in northern Virginia and placed his luggage in the car's trunk. Then a Honda blocked him in and two black-clad men in hoods emerged, smashed his windows with a pistol and robbed him of roughly $350,000 in jewelry.

It was a crime that repeated itself for months as thieves working in concert swiped millions of dollars in merchandise from other salesmen, in bold and sometimes violent heists in locations including a New York City taxicab, outside a Holiday Inn in North Carolina and at Newark Liberty International Airport.

A case in federal court in Virginia underscores the perils faced by traveling jewelry salespeople and the ambitious efforts by law enforcement to catch the thieves. It's not a new threat, but keeping salesmen safe remains a persistent challenge as the criminal gangs have grown more sophisticated and violent.

"In the last decade, there seems to be a trend toward more sophisticated criminal enterprises," said FBI Special Agent Eric Ives, who's in charge of the bureau's major theft program. "It's not a locally based crime problem anymore."

The crimes follow a familiar pattern.

Thieves working together case jewelry stores in search of a salesman – often a well-dressed man carrying a large case – and tail him to the next destination, sometimes for hours. They confront the salesman, frequently slashing car tires, punching out windows, grabbing gems and maybe the courier's phone and keys, too.

Authorities say the eight men and women in the Virginia case are part of a so-called South American theft group, a label typically applied to Colombian criminals who menace salesmen. They're accused of at least 15 robberies and two car break-ins totaling about $4.6 million in jewelry, mostly along the East Coast. The majority of robberies occurred as couriers arrived at or departed from hotels.

Seven were charged in March after an extensive Bureau of Alcohol, Tobacco, Firearms and Explosives investigation that relied on cell phone and bank records, undercover surveillance, E-Z Pass and GPS travel tracking – even a decoy salesman sent into stores to gather intelligence. An eighth person has since been indicted. They have pleaded not guilty and face trial in November.

"It was a highly sophisticated ring. It was a tight-knit group. It was a group that did their homework," said Neil MacBride, the U.S. Attorney for the Eastern District of Virginia, which is prosecuting the case. "They were very patient. They were extremely mobile. They could strike quickly when they had to – and they were dangerous."

Jewelry salespeople have long made easy targets. Robbing a lone salesman in a parking lot is less risky than holding up a store and stolen jewelry, which can be sold on the black market at marked-up prices, converted into cash or melted down for future use, is difficult to recover. The FBI says only 4.2 percent of jewelry and precious metals stolen in 2010 were recovered, compared to 56.1 percent of stolen vehicles. In the Virginia case, authorities say, the jewelry was fenced in New York through Russian brothers who owned a jewelry business.

Off-premises attacks, primarily against traveling salespeople, dropped from 113 to 78 between 2010 and 2011, partly because of a declining number of salesmen and more aggressive law enforcement, according to the Jewelers' Security Alliance, a trade group. But the crimes have become more violent, escalating from quick bag-snatch thefts to robberies that sometimes end in beatings – or worse.

One salesman was killed in Huntsville, Texas, last year when thieves trying to escape ran him over with their car. The owner of a Connecticut jewelry manufacturer was killed in December and an associate wounded in what police called a targeted robbery.

"I think that salesmen have become far more aware of the risks and they don't fall for the trickery as easily as they did in past years," JSA president John J. Kennedy said, explaining increased violence. "So if the trickery doesn't work, that's what you do."

Leon Rozio, 68, retired after being robbed of more than $160,000 during a 2008 heist in the parking lot of a Boca Raton, Fla., jewelry store. A group of men approached his car as he waited outside for his partner and busted out the windows. One reached in and grabbed a bag of jewelry. Rozio fired his pistol at their car, which he said tried to run him over. One robber was fatally wounded, but Rozio wasn't charged because the shooting was deemed self-defense. He retired at his family's urging.

"I figured they were right," Rozio said. "These people, they have guns ... killing and all of that stuff. I had to go into retirement."

An 89-page affidavit filed in the Virginia case details a cat-and-mouse game in which the suspects are alleged to have played different roles, from coordinating with fences to surveillance to doing the robberies. The investigation revealed a level of criminal street smarts and sophistication, authorities say, as the suspects regularly switched cars and license plates and made structured cash deposits in various bank accounts. When they became suspicious they were being followed, they began communicating with a new batch of cell phones.

Some salesmen were apparently caught by surprise even though they were tracked for miles and across states. One salesman robbed in November 2010 outside his Rutherford, N.J., home had been followed since leaving Philadelphia earlier in the day, with cell phone and E-Z Pass records showing the victim and suspects traveling the New Jersey Turnpike and crossing the George Washington Bridge at nearly identical times.

Investigators countered with their own techniques.

Besides surveillance, agents also used phone and travel records to track the suspects to precise locations. Last fall, the ATF also sent a decoy salesman into a Virginia Beach jewelry store and waited for the undercover agent to be followed, deploying a SWAT team to a nearby hotel in case the suspects tried to rob him.

Though the investigation was successful, Kennedy said it illustrated that the industry remains dangerous.

"The risk is tremendous, and you have to be alert and security-minded 24-7," Kennedy said. "You are not just a risk in downtown L.A. or leaving New York. You're at risk anywhere."