A former fighter for the Revolutionary Armed Forces of Colombia, or FARC, Mr. Saldarriaga was believed to have coordinated the assassination of two former members of the United Self-Defense Forces of Colombia — a right-wing paramilitary group that acts as security for traffickers — in the parking garage of a Buenos Aires shopping mall in June 2008, the Argentine authorities said.

But then, the police said, Mr. Saldarriaga may have betrayed his boss by losing or stealing half a ton of cocaine. Another theory is that Mr. Saldarriaga had tried to branch out as a trafficker in his own right in an area of Argentina controlled by Mexico’s Sinaloa drug gang and was punished for trespassing.

Mr. Saldarriaga is by no means the only notorious foreigner involved in the drug trade to make the news. Days before Mr. Saldarriaga was killed, Ruth Martínez Rodríguez, a Colombian who was once married to Mr. Barrera, was arrested in an upscale suburban home outside Buenos Aires, accused of fronting a business that tried to export 280 kilograms, or about 617 pounds, of cocaine to the United States, Europe and Asia hidden in Louis XV-style furniture. From Nordelta, a gated community with a private golf course, Ms. Martínez was said to have laundered money through real estate and a furniture business.

Because she was pregnant, she was sentenced to house arrest.

In another episode, in 2010, Argentine security officials arrested Angie Sanclemente Valencia, a onetime Colombian beauty pageant winner, on suspicion of running a ring of drug-smuggling models, including a 21-year-old Argentine woman who was caught trying to fly to Cancún, Mexico, from Buenos Aires with 55 kilograms, or about 121 pounds, of cocaine in her checked luggage. The young woman gave up information on Ms. Sanclemente, who was tracked down, with the assistance of Interpol, five months later at a Buenos Aires youth hostel and is currently serving a prison term of six years, eight months.

With drug gangs looking to expand their operations, Argentina, which was a transit point in the 1990s, has turned into a profitable marketplace. There is a huge local demand for drugs. And unlike governments in some other countries in the region that are engaged in aggressive drug wars, the government here has not yet aimed the full might of its military on traffickers.