Two gang hit men admitted to Mexican authorities that they killed 17 of 43 students that had been missing in southern Mexico for a week, after 28 bodies were found in a mass grave.

The chief prosecutor of the often-violent Guerrero state said it would take 15 days to identify the bodies found in the grave, some of which had been burned and dismembered, according to a report from Yahoo News.

The missing students are alleged to have hijacked the buses and were shot at by Iguala police officers. Inaky Blanco, the Guerrero prosecutor, said the Guerreros Unidos gang played a part in the violence on Sept. 26 that left six people dead, 25 injured and 43 missing.

Blanco said the night's activities remain under investigation, but if the students were killed, it would be one of the worst mass killings since Mexico's drug war picked up in 2006.

Blanco said that 29 suspects have been identified so far, 26 of whom have been arrested, including Felipe Flores, the head of security for Iguala, according to ABC Australia.

Local police had been infiltrated by Guerreros Unidos, and that Flores had conspired with a gang leader to order the killings, Blanco said.

The mass grave was found on a hillside in Pueblo Viejo, a poor part of the city of Iguala, where the students were last seen.

"A bed of branches and tree trunks was made, on which the bodies of the victims were laid and a flammable substance was used," Blanco said.

On Sunday, parents of the missing students and fellow students from the education training college blocked the highway between the capital of Guerrero, Chilpancingo, and Acapulco, protesting the Mexican authorities.

Some parents said they has seen photos of the bodies found in the mass graves and that they didn't think it was their children.

"As parents, we reject this situation. It's not the youngsters. We know they're holding them alive," said Manuel Martinez, whose son is among the missing.

Relatives of the missing students have given police DNA samples to see if they match the bodies found in the mass grave. Blanco said the search for the missing would continue until a search is no longer necessary.