In 2018, a hacker hired by the Mexican Sinaloa drug cartel run by the infamous kingpin Joaquín “El Chapo” Guzmán spied on the U.S. Embassy in Mexico City with the goal of identifying “people of interest” for the cartel to target and kill, according to a new U.S. government watchdog report.

The Sinaloa drug cartel in Mexico hacked the phone of an FBI official investigating kingpin Joaquín “El Chapo” Guzmán as part of a surveillance campaign “to intimidate and/or kill potential sources or cooperating witnesses,” according to a recently published report by the Justice Department.

The stunning new details offer a rare look at how technology can be exploited in the high-stakes battle between US law enforcement and the violent Mexican cartels that control illicit drug trade.