For more than three years, U.S. Immigration and Customs Enforcement had an inside man in one of Mexico's most notorious drug cartels. Informant No. 913, Guillermo Eduardo Ramirez Peyro — better known by his nickname, Lalo — was a former Mexican highway patrolman who had joined the drug trade in the mid-1990s and was rising up the ranks of the Juarez drug cartel. With Lalo's help, ICE set its sights on nabbing the cartel's third in command. At the same time, Lalo was helping the cartel's henchmen kidnap, torture and kill rivals. Critics say ICE officials knew what Lalo was up to — and did nothing to stop him. Below, a timeline of Lalo's criminal activities and what U.S. officials knew about them — including details newly uncovered by NPR.