At least 80 sets of human remains have been unearthed so far, and authorities are investigating whether recently discovered mass graves contain 43 students who vanished more than two weeks ago.
Residents of Iguala now call the minibus that travels to the Las Parotas stop the "combi of the cemetery." Nearby, 28 badly burned bodies were found inside five burial pits on October 4.
On another hill, four more unmarked graves with an undisclosed number of bodies were discovered last week after suspects said some of the missing students were buried there.
Some 200 kilometres south of Mexico City, Iguala lies in the state of Guerrero, one of Mexico's poorest regions and beset by violent drug gangs.
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As authorities dig up the bodies, the 140,000-population city's dirty secret is being exposed: Its police force is accused of being in cahoots with the Guerreros Unidos gang.
"We see an association (of the gang) with municipal employees," Attorney General Jesus Murillo Karam said last week.
Prosecutors have detained 26 gang-linked police officers accused of shooting at busloads of students on September 26 in a case that has sparked national outrage and international condemnation.
Four gang members were also detained over the night of violence that left six people dead and 43 of the apprentice teachers missing.
The mayor, his wife and the police chief have gone into hiding as investigators seek to question them over attack, whose motive remains under investigation.