A Mexican cartel hacker used an FBI agent’s phone records and public cameras to track down and intimidate — and even kill — government informants, according to a startling new report.

The hacker — hired by the vicious Sinaloa cartel led by Joaquín “El Chapo” Guzmán — broke into the phone of an FBI assistant legal attaché stationed at the US Embassy in Mexico City, and was able to extract an alarming amount of information that led the criminals straight to government informants.

It remains unclear exactly when the hacking operation happened or how long it lasted, but it was revealed in a recent FBI audit investigating how the bureau can battle new technology threats, Reuters reported.