TIJUANA, Mexico — The bodies of 11 men and one woman were found dumped in an empty lot next to a Tijuana elementary school yesterday morning, an hour before children were scheduled to arrive.

City officials suspended classes after finding the victims, most of whom had been bound and tortured. Some were only partially clothed, a state police spokeswoman in Tijuana, Prisna Perez, said.

Minutes after the grisly discovery, four other bodies were found in another empty lot in Tijuana, and two other bodies were discovered late Sunday in a lot next to a factory.

Investigators believe 16 of the victims were killed by warring drug gangs. The other two were victims of street crime, Jose Manuel Yepiz, a spokesman for the Baja California attorney general’s office, said.

The director of the Binational Center for Human Rights, Victor Clark Alfaro, said the killings come as the Arellano Felix cartel suffers internal strife and seeks to fend off Joaquin “El Chapo” Guzman’s push into the region.

Yepiz said the 12 bodies were discovered next to a message written on a white piece of cardboard that read, “This is going to happen to all of those who are with the engineer for being blabbermouths.”