On Saturday, 28 charred bodies were found in a mass grave on the outskirts of a town in southern Mexico where a group of student protesters went missing after police opened fire on them in late September.

Prosecutors have since uncovered ties between organized crime and the local police and city government of Iguala, a town 125 miles south of the capital, Mexico City. The mayor of the town and its security chief have disappeared, evading warrants for their arrest.

After eight members of the Guerreros Unidos gang were arrested, they tipped off authorities on the location of the mass grave, uncovered Saturday in a poor district on outskirts of Iguala.

“They grabbed 17, took them to the top of a hill in Pueblo Viejo where they have clandestine graves and where they say they killed them,” state prosecutor Inaky Blanco said Sunday, according to Agence France-Presse. Blanco cautioned those details haven’t been confirmed by investigators. “El Chucky,” the gang’s feared leader, ordered the hit, but the motive still isn’t clear, Blanco added.

Iguala is a gateway to the Tierra Caliente, a lawless region where vigilantes do battle with powerful Mexican drug cartels. “This is the land of the wicked,” a resident named Jose Garcia told AFP. Garcia said he saw police going up the hill to the site where the mass grave was found, a mile from the nearest road on steep hillside thick with vegetation.

The bodies were found on a bed of branches and tree trunks that had been set ablaze. It could take more than two weeks to identify the disfigured corpses with genetic testing, Blanco said, declining to speculate whether the bodies were those of 43 students from the Ayotzinapa Normal School teacher’s college who went missing Sept. 26.

They came to Iguala to raise funds for a planned protest against hiring practices that, in their view, favor urban students over rural ones.

According to the Associated Press, these students and others in Mexico’s rural teacher’s college system are radicals whose militant protests often include hijacking buses and delivery vehicles. This isn’t their first clash with law enforcement. In 2011, two Ayotzinapa students died in a police confrontation after they allegedly hijacked buses and blocked roads as a means of protest. They reportedly set fire to a gas station, killing an employee.

On Sept. 26, members of the student union told the BBC, they were just trying to hitch a ride back to their college on local buses. However, authorities claim they commandeered the buses by force. Blanco said Iguala’s public security director, Francisco Salgado Valladares, enlisted members of the Guerreros Unidos gang to force students off the bus, according to AFP.

As the students sped away, the police opened fire. The attack intensified when the buses stopped and unarmed students got off, the Guardian reported. Some fled, while roughly 20 others were taken away in patrol cars.

Three were killed. One body was found with his face skinned and his eyes gouged out, the Guardian reported. Another 25 were wounded.

About three hours later, masked gunmen opened fire again on a few students who had returned to the scene and were talking to reporters. Stray bullets felled three innocent bystanders — the driver of a bus carrying a soccer team, a 15-year-old player and a woman in a taxi.

“We thought somebody was letting off fireworks at first, with the bangs and the flashes from the machine guns lighting up the darkness,” the team’s trainer, Facundo Serrano, told the newspaper Milenio.

The unrest continues in the wake of the bloodshed. On Saturday, students from Ayotzinapa threw Molotov cocktails and overturned a car outside the governor’s home in the state capital of Chilpancingo after state officials barred them from visiting the graves and viewing the bodies, the AP reported.

On Sunday, their parents joined the protest, blocking the highway between Mexico City and Acapulco. They said they had seen pictures of the recovered bodies and didn’t believe they were those of their children. “We know they’re holding them alive,” Manuel Martinez, whose son is missing, told AFP.

So far, 29 people have been charged in the case, including 22 police officers.

According to the AP, Mexico’s National Human Rights Commission is investigating human rights abuses including extrajudicial executions and forced disappearances by Iguala city police.