How El Chapo’s sons built a fentanyl empire poisoning America

In January 2017, days after Mexico extradited the notorious drug trafficker Joaquín “El Chapo” Guzmán to the United States, local cops in his home state of Sinaloa fell under attack.

Some were shot dead in broad daylight. Others vanished and were never found. In all, 13 police officers died or disappeared in the months that followed.

That spree was the start of a shift in tactics within Guzmán’s Sinaloa Cartel, according to four intelligence and security officials, one that signaled the arrival of a new force inside one of Mexico’s...