Signs with the faces of the missing students of Ayotzinapa is seen while students block access to the Mexican Attorney General's office during a demonstration to ask for justice for the 43 missing students from Ayotzinapa in Mexican state of Guerrero, on November 06, 2014 in Mexico City, Mexico. Former Mayor of Iguala Jose Luis Abarca and his wife Maria de los Angeles Pineda were captured on Tuesday by Federal forces in Mexico City. They are both suspected as masterminds of the disappearance of the students. Miguel Tovar/LatinContent/Getty Images

The 43 students who went missing in southwestern Mexico six weeks ago are believed to be dead after human remains were found in a river and its river banks, Mexico’s attorney general, Jesus Murillo Karam, said on Friday.

Three detained gang members, who were caught one week ago, confessed to burning the group of bodies in a dump near Iguala in the Mexican state of Guerrero, said Murillo Karam at a press conference. The suspects testified to loading the students in dump trucks and burning them in a funeral pyre along the River San Juan in Cocula. Once their ashes had cooled, they were placed in garbage bags and dumped in the river.

The students, who attended a teachers college, had been protesting discriminatory hiring practices in Iguala on Sept. 26. It is believed that they were then kidnapped by police on orders of the local mayor, who worried they would disrupt a speech his wife was giving and wanted to “teach them a lesson.” The police then handed the students over to the gang that killed them and burned their bodies.

Since capturing the three gang members, 74 other individuals, including dozens of police, have been detained in the investigation.

In the news conference, Murillo Karam also said that investigators would have to identify the victims using DNA evidence, which would be incredibly difficult as the bodies were badly burned and many of the victims’ teeth had “turned to powder.”

"They didn't just burn the bodies with their clothes, they also burned the clothes of those who participated," Murillo Karam said. "They tried to erase every possible trace."

The kidnapping has sparked protests all over the country and have called into question President Enrique Pena Nieto’s claims that Mexico was becoming safer since he took office two years ago. More than 100,000 people have been killed in violence linked to organized crime since 2007.

"To the parents of the missing young men and society as a whole, I assure you that we won't stop until justice is served," Pena Nieto said.