Even in crime-ridden Guatemala, the headlines were startling: Prosecutors busted a customs bribery ring that likely defrauded the state of millions of dollars, with the current and former Tax Authority chiefs and a top aide to the vice president implicated.

The wiretaps, raids and 20 arrests announced last week were the fruit of a probe by prosecutors and by the U.N. International Commission Against Impunity in Guatemala, which was set up to investigate and prosecute organized crime and its pernicious influence over the government and judicial system.