The Mexican Sinaloa drug cartel hired a hacker to track and surveil the FBI, then used that information to intimidate and even kill witnesses.

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 hacker was able to break into the agent’s phone remotely and watch their incoming and outgoing calls, and even monitor the phone’s geolocation.