Mexican marines guard the site where an unspecified number of bodies were found in clandestine graves. (Agence France-Presse)
The lush hills surrounding the southern Mexican town of Iguala have been used by criminals to bury scores of victims beneath the green canopy this year alone.
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.
"Most people knew that mass graves existed. I don't know why the government did nothing about those that were found before," said Jorge Popoca, leader of the Iguala's shopkeepers association.
Some 200 kilometers (125 miles) south of Mexico City, Iguala lies in the state of Guerrero, one of Mexico's poorest regions and beset by violent drug gangs.
As authorities dig up the bodies, the 1,40,000-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.
Anger over the case boiled over on Monday as fellow students torched a Guerrero state government building in the capital Chilpancingo, demanding Governor Angel Aguirre's resignation.
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.
The students say they went to Iguala to raise funds for their studies, though authorities say they seized the buses to return home, a common practice among the state's radical aspiring teacher.
- 'Awful screams' -In the neighborhoods near the mass graves, residents say they have been afraid to leave their homes at night for years because criminals brought victims up those hills after dark.
One resident, Beto Garcia, said he could sometimes hear "the awful screams of men."
"One time, you could clearly hear a person. It sounded like they were cutting him up with machetes. You could also hear two others laughing," Garcia said.
Another resident pointed to the hill where 28 bodies were found and said he saw police in the area the week that the students disappeared.
"There are eyes everywhere," the resident said, explaining why he was afraid to give his name.
Townspeople say the Guerreros Unidos have hideouts in caves high up in the mountains.
Down in the city, the gang made businesses pay what it calls a "tax."
"They charged 1,000 pesos ($73) per week to tenants at the market. If they didn't pay they kidnapped them," said Rosa Caballero, a 20-year-old candy seller.
The authorities say the gang's main source of revenue is the sale of marijuana and heroin in the United States.
The Guerreros Unidos, an offshoot of the bigger Beltran Leyva drug cartel, has been at war with Los Rojos and other gangs in Guerrero.
Well before the latest mass graves were discovered, 21 bodies were unearthed just north of Iguala in February and another 31 in its outskirts, including 27 between April and May, according to investigators.
While federal forensic experts are examining the most recent remains, the city morgue is overwhelmed with 30 unidentified corpses lying in the freezer for three months, an employee said.
Many of the unclaimed bodies found in Iguala end up at the municipal cemetery's official mass grave without any investigation, the morgue employee said.
Families used to ask for bodies to be exhumed to identify them, said gravedigger Carlos Ulises Cambron.
But they no longer come, he said, "because the murders are hideous. The families don't recognize them."