IGUALA, Mexico (AP) — Revelations of mayhem, murder and mass graves have shed light on another deeply troubled region of Mexico, the southern state of Guerrero, where federals officials on Monday disarmed local police and took over security after an attack on students that left at least six dead and 43 missing.

Officials say that police officers were in league with a local gang called the Guerreros Unidos in carrying out the attack, and sent a new preventative unit of the federal police to keep order and help look for the missing.