A Mexican police chief has quit after criminal gangs made a chilling demand: resign or we will kill more local officers. Roberto Orduna announced he was leaving hours after gunmen killed a police officer and a jail guard and left signs on their bodies saying they had fulfilled a promise made on Wednesday to murder at least one officer every 48 hours until Orduna quit. The killings are a sign that gangs are determined to control the police force of the Mexican border city of Ciudad Juarez, a major entry point for drugs heading into the US.