Mexican authorities discovered a new mass grave late Monday, about 10 miles from where 43 college students went missing. Forensic experts are testing human remains at the site to assess if they belong to the young men last seen in police custody in the town of Iguala last month

Federal authorities came upon the new location, in the town of Cocula, based on statements from four members of the Guerreros Unidos gang who were arrested early Monday, according to a government official who spoke on condition of anonymity because he was not authorized to speak to the press.

Attorney General Jesús Murillo Karam confirmed the four arrests in a press conference but made no mention of more remains or mass graves. He said some of those arrested could be members of the Guerreros Unidos criminal organization responsible for the disappearance of the students after an attack by local police. Two of the detainees said they received a large group of people around Sept. 26, the date the students went missing, Murillo Karam said.

The disappearances have sparked outrage across Mexico, with thousands marching in cities across the country in recent weeks as they call for the students’ safe return, and with universities organizing strikes in solidarity with the missing.

Students from Ayotzinapa teachers school, a rural teacher training center that caters to poor and indigenous people, were protesting government education reforms on Sept. 26 when local police officials opened fire on demonstrators, killing three students and three bystanders. In the aftermath, 43 students disappeared.

Ayotzinapa students have long been characterized by Mexico authorities as radical, and are known for protesting protesting government reforms that they say target the poor. Guerrero state, one of Mexico’s poorest, is home to self-defense, vigilante groups formed in response to decades of state and organized crime.

Following the disappearance of the students, dozens of police officers were arrested after the leader Guerreros Unidos revealed that the police had handed over some of the students to the group and ordered their executions. Further confessions, including from police officers, reiterated the collaboration between police and the gang.

As of Tuesday, there were 56 people in custody in the case. Mexican authorities said they have mounted searches for the students, spurred by increasingly violent demonstrations that included the burning of Iguala's city hall by protesters last week.

But students say there is government complicity in the crimes, accusing local and federal authorities of corruption. They say that Guerrero Governor Ángel Aguirre, who stepped down last week under criticism over the state's handling of the case, had for years ignored Iguala mayor José Luis Abarca's corruption and gang ties. And they blame what they call the federal government’s neo-liberal reforms for starting the protest movement in the first place.

Before Monday's discovery, investigators had found a total of 11 clandestine graves containing 38 sets of human remains in the hills of Pueblo Viejo in the municipality of Iguala. Initial DNA testing of the remains determined the bodies were not those of the missing students and officials were waiting for results of second round of tests.

With wire services