“I’m very small-time,” he told the arresting officer. “I work by myself.”

By then, Guardarrama was a married man and the father of a young daughter. The couple divorced four years ago. His ex-wife did not respond to telephone messages.

State business records show that in 1996, Guardarrama helped to start a business called Plastic Air Freshener in downtown Miami. The office was a block from the Seybold Building, 36 NE First St., a hub of diamond and jewelry commerce in Miami. It is unclear what Guardarrama’s business did, exactly, but in 1997 he reported earning about $200 per month as a jewelry seller, according to police records.

Jewelers at the Seybold building say Guardarrama had been in the wholesale diamond and gold business for close to two decades. He was a friendly guy with a good reputation, a seller who visited routinely to sell them jewelry they then sold in their own stores.

None of them could believe the allegations against Guardarrama. Authorities say he coordinated two groups of jewelry thieves that have operated in South Florida and across the country since at least 2005.

Stealing diamonds is a lucrative, age-old business, said Steven Wexler, president of the private Wexler Insurance Agency, which covers the industry. At the national level, hundreds of millions of dollars worth of precious stones and gold are stolen each year in the United States, he estimated. His own Coral Gables-based agency reported $50 million in losses last year.

“Thefts have increased in the past few years, and many blame the economy,” he said. “South Florida has been hit especially hard, mostly because of the Colombian gangs.”

Guardarrama worked with these groups of thieves who live in Colombia but travel to Miami and other U.S. cities to commit robberies, authorities say. He was one of a few fences who helped the thieves follow traveling diamond dealers who sell their wares in the Seybold building, according to the sworn testimony of convicted thieves.

“Sometimes a person who is in the jewelry business, Mr. Juan Guardarrama, called us to tip us about the victims,” Andrés Felipe Lema told authorities under oath. “We followed jewelry/diamond representatives around, waiting for them to stop at gas stations, hotels, restaurants, jeweler stores or pawn shops. At those places we attacked them.”

During a typical assault, the crew would break through a dealer’s car windows or slash his tires, often while the dealer was still inside. Then they would grab the bags of jewelry and run.

The second crew of diamond thieves, mainly Cuban-born welders, ransacked jewelry stores after hours. One thief, Tony Adrián Sánchez Estrada, gave a sworn statement explaining that the group used metal cutters to open holes in stores’ ceilings that they could then drop through. Once inside, they deactivated the alarms. Finally, one of the welders would use a blowtorch to enter the safe.

“That took about almost three hours, four hours, more or less,” said Sanchez, who once worked as a welder on boats in Cuba.

After the heists, authorities say, both groups would call Guardarrama or another of the fences involved in the criminal enterprise. They would meet with Guardarrama in Miami Beach hotel rooms, at his downtown Miami apartment or even in his mother’s modest duplex in Sweetwater, according to the allegations.