IGUALA, Mexico (AFP) - Hitmen linked to police have confessed to murdering 17 of 43 missing students in southern Mexico as relatives of the victims refuse to believe they may have been buried in a mass grave.
Authorities discovered over the weekend six adjoining pits containing 28 bodies, some badly burned and in pieces, on a hill outside the Guerrero state city of Iguala, where the students were last seen.
Witnesses say several students, who are from a teacher training college known as a hotbed of radical protests, were whisked away in police vehicles on the night of September 26 after officers shot at their buses.
Inaky Blanco, the chief prosecutor of violence-plagued Guerrero state, said late Sunday that it would take between two weeks and two months to confirm whether the bodies belong to any of the missing students.
But he said two hitmen admitted to executing 17 of the students in the same Pueblo Viejo district where the clandestine grave was found, some 200km south of Mexico City.
The case could become one of the worst slaughters that Mexico has witnessed since the drug war intensified in 2006, leaving 80,000 people dead to date, and the most horrific since President Enrique Pena Nieto took office in December 2012.
Parents of the missing students, however, said they believe Guerrero state authorities are lying to them.
Some of the parents said they were shown pictures of the bodies but that they did not believe that they looked like their children.
"Everything that has been said, that the boys have appeared (dead), is a lie," said Maria Castrejon, whose nephew is among the missing. "The boys are alive. We as families know this, we feel them." Parents and hundreds of students blocked the highway between the state capital Chilpancingo and Acapulco in protest on Sunday, voicing anger at how Governor Angel Aguirre has handled the case.
Blanco said the Guerreros Unidos gang participated in a night of violence on September 26 that left six people dead, 25 wounded and 43 missing after attacks on the student buses and another one carrying a football team.
Some 30 people have been detained over the shootings, including at least 22 police officers. Authorities have sought to question the town's mayor and security chief, both of whom have disappeared.
While the students are said to have hijacked buses to return home that night, Blanco said the motive for the attack remains under investigation.
Two of the gang's hitmen told investigators that they were ordered by Iguala's public security director to head to the site of the bus shootings, Blanco said.
The two hitmen then received instructions from a Guerreros Unidos leader known as "El Chucky" to take the students and kill them, he said.
"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," Blanco said.
The mass grave was found following the interrogations of suspects.
But the prosecutor said authorities will not know whether the bodies belong to the missing students for at least 15 days.
The bodies were placed in a "bed" of tree trunks and set on fire with a flammable substance, he said.
Relatives have given DNA samples to see if they match the bodies in the mass grave, while Blanco said the search for the missing would continue as long as the identities are not confirmed.
At the request of student leaders, an independent team of Argentine forensic specialists has been asked to help identify the bodies.
Survivors said the students had gone to Iguala to conduct fundraising activities and came under attack by police after they boarded three buses.
Oscar Garcia, 17, said his family was aching over the disappearance of his brother, who wanted to become a teacher of Spanish and indigenous languages.
"He wanted to be a bilingual teacher, Mixteco and Spanish," Garcia said. "As a family, we feel terrible without knowing anything about where they are."