Wachovia [Bank] ... made a habit of helping move money for Mexican drug smugglers. San Francisco's Wells Fargo & Co., which bought Wachovia in 2008, has admitted in court that its unit failed to monitor and report suspected money laundering by narcotics traffickers - including the cash used to buy four planes that shipped a total of 22 tons of cocaine. The admission ... sheds light on the largely undocumented role of U.S. banks in contributing to the violent drug trade that has convulsed Mexico for the past four years. Wachovia admitted it didn't do enough to spot illicit funds in handling $378.4 billion for Mexican currency exchange houses from 2004 to 2007. That's the largest violation of the Bank Secrecy Act, an anti-money-laundering law, in U.S. history - a sum equal to one-third of Mexico's current gross domestic product. Wachovia's blatant disregard for our banking laws gave international cocaine cartels a virtual carte blanche to finance their operations," said Jeffrey Sloman, the federal prosecutor who handled the case. "It's the banks laundering money for the cartels that finances the tragedy," said Martin Woods, director of Wachovia's anti-money-laundering unit in London from 2006 to 2009. Woods says he quit the bank in disgust after executives ignored his documentation that drug dealers were funneling money through Wachovia's branch network. "If you don't see the correlation between the money laundering by banks and the 22,000 people killed in Mexico, you're missing the point," he said.