Mexican police have found five decomposing heads left in a sack outside a primary school in Acapulco

Handwritten messages were also found, reportedly threatening the state governor as well as local drug lords. It was not clear if the discovery of the heads and five decapitated bodies elsewhere in the city was linked to extortion threats against teachers. Dozens of schools have been closed after teachers went on strike over security concerns. Police were called to a street in the Garita neighborhood of Acapulco. There they found a sack inside a wooden crate placed near the school, officers said. Inside were the heads of five men, as well as the threatening messages. Police had earlier discovered five headless bodies in another part of the city, left either inside or near a burned-out vehicle. Acapulco, on Mexico's Pacific coast, has seen several episodes of gruesome violence as drug gangs fight for control of the resort city. But as the government crackdown on cartels continues, criminal organizations here and in other parts of Mexico are fracturing and increasingly turning to extortion. Recently, as the new school year began, dozens of teachers in Acapulco said that criminal gangs had threatened them with violence if they did not hand over half their salaries from October 1, 2011. They and colleagues have since been on strike, leading to the closure of more than 100 schools.