Minutes after seven in the morning, Dolores was about to arrive at the entrance booth of the Social Reinsertion Center (Cereso) 3 to visit her son, who had been imprisoned for three years for crimes against health. Suddenly, at least 12 men armed with assault rifles and tactical equipment burst in, shouting, "Everybody down!" They killed two guards at the entrance and hurt two people who were related to the prisoners.
The killers may have been part of the Los Mexicles gang, which is part of the Gente Nueva group. Gente Nueva is the armed and operational arm of the Sinaloa cartel. They broke into six vans, some of them armored, just as the New Year's Eve visit to the inmates was beginning. In no more than 10 minutes, they killed 10 guards and five inmates and injured 12 people (prisoners, guards, and civilians); their objective was to free 24 convicts from their criminal organization.