Proceedings are under way to extradite Joaquín Guzmán Loera, the cartel boss who twice escaped Mexican prison, to the United States. If El Chapo, as he is known, goes to trial in Chicago, the government has star witnesses lined up to testify against him: the identical twins Pedro and Margarito Flores. While still in their twenties, the Flores brothers became major drug traffickers, importing tremendous quantities of drugs. They avoided violence and feuds with rivals as their power grew. But they got caught in the middle of a cartel war and found themselves in a dangerous, maybe impossible position. That’s when they started working secretly for prosecutors, recording their business calls with El Chapo and others in exchange for leniency in their own trials. Tom Shakeshaft, the former assistant U.S. attorney who flipped them, tells Patrick Radden Keefe how it happened.