And the Mexican Congress, after years of government inaction on the issue, is weighing a series of legislative proposals based on Calderon's anti-laundering package that would make it more difficult to cleanse dirty money. In the meantime, the restrictions on the use of U.S. cash in Mexico appear to be altering the flow of drug-tainted dollars for the first time, officials on both sides of the border say.
Under the proposed legislation, a specialized unit added to the attorney general's office, with advice from U.S. officials, would be authorized to take the lead in money-laundering cases and inspect a wide variety of businesses in search of illicit profits.
In addition, the government nearly a year ago replaced the Finance Ministry official in charge of such cases with a veteran Washington-based diplomat, Jose Alberto Balbuena, who had spent many months working with U.S. financial officials and is said to have a better grasp of what's at stake and a good working relationship with top prosecutors.
To date, Mexican reporting requirements have applied only to banks. Under legislation approved by the Senate last year and now before the lower Chamber of Deputies, a range of other industries would also be required to report large cash or suspicious transactions using unexplained funds.
These include real estate, car dealerships, betting parlors, art galleries, notaries, and, possibly, religious institutions. Mirroring "know your customer" regulations in the banking world, the rules would require disclosure of cash purchases for more than 200,000 pesos, or about $14,000, of numerous goods and place a cap of 1 million pesos, or about $70,000, on cash purchases of real estate.
Law enforcement experts say the proposed legislation could fill a yawning gap in Mexico's crime fight.
"It's going to counteract the financial and economic power of the criminals," said Ricardo Gluyas, a professor at the National Institute of Criminal Sciences, which trains Mexico's organized-crime prosecutors. "The new law has teeth. It covers a broad spectrum."
One potentially powerful tool, an asset-forfeiture law that allows authorities to seize property and accounts of traffickers and launderers, was approved by Congress in 2008. A similar law made a big difference in crime fights in Colombia and Italy, allowing authorities in those countries to confiscate and resell properties of drug traffickers and Mafiosi.
"Without firing a shot, you can generate a lot more results by seizing the fortunes of the big capos," Gluyas said.
But critics say the Mexican asset-forfeiture law threatens the due-process rights of owners. So far, it has been little used: Courts had approved only two cases by late this summer, with more than a dozen pending.
Perhaps more than any other measure, the government's move last year to restrict bank deposits of U.S. cash appears to have slowed the entry of dollars to Mexico's financial system. Bank-account holders were no longer allowed to deposit more than $4,000 a month.
In response, traffickers and their launderers are shifting tactics, including keeping money in the United States, officials say. And U.S. officials say that since Mexico announced the new rules, more money appears to be going elsewhere, especially to the Caribbean and Guatemala, where officials have detected a surge in circulating U.S. bank notes.
"That's the big question," Balbuena said. "Where is the money?"
A possible explanation can perhaps be gleaned from an Oct. 5 incident: Customs inspectors in Tijuana stopped an armored car full of plastic bags stuffed with $915,000 in cash. There was no documentation for the money, law enforcement sources familiar with the discovery said.
But it wasn't headed into Mexico. It was headed north, into San Diego.
Cecilia Sanchez of The Times' Mexico City bureau contributed to this report.
This is one in a series of occasional articles.