MEXICO CITY (AP) — Families of 43 students who were kidnapped in southern Mexico on Sept. 26, 2014 are still demanding answers about their sons' whereabouts as the sixth anniversary of the crime approaches.

Relatives gathered Thursday outside Mexico's Supreme Court, holding photos of their missing sons and banners demanding justice.

Some of the lawyers in the case hope that a new investigation report to be released on Saturday's anniversary will include information on federal police or soldiers' possible involvement in the mass abduction.

“There is enough proof to proceed against these people,” said Santiago Aguirre, a lawyer for the PRODH human rights center, noting that new testimony and tracing records of cellphones backed up the theory that “without doubt, they were part of the scheme.”

The 43 students from the rural teachers college at Ayotzinapa in the southern state of Guerrero were abducted by corrupt local police in the town of Iguala. They were then allegedly turned over to a local gang that killed them and purportedly burned their bodies.

But burnt bone fragments found near a local garbage dump have been matched to only two of the students.

Clemente Rodríguez is the father of one of the two students whose DNA profiles matched some of the bone fragments. But Rodríguez is still demanding to know exactly what happened and who was responsible for the death of his son, Christian Alonso.

“They have to give us something concrete, some progress,” said Rodriguez.

Many of the suspects arrested in the case were later released, and many claimed they had been tortured by police or the military. In March, a judge issued an arrest warrant for Tomas Zerón, the former head of investigations for the Attorney General’s Office, for alleged violations in the investigation of the case.

Zerón and five other former officials face charges including torture, forced disappearance and judicial misconduct.

Zerón was at the center of the government’s widely criticized investigation, which has failed to definitively determine what happened to the students. Two independent teams of experts have cast doubt on the insistence of Mexican officials that the students bodies were incinerated in a huge fire at the trash dump.

The students attended the Rural Normal School of Ayotzinapa. They were in Iguala to hijack buses to use for transportation to a rally in Mexico City.

They were attacked on the buses by local police and allegedly handed over to members of the Guerreros Unidos cartel, some of whose members confessed to killing them and burning the bodies.

Implicating soldiers in the case would be difficult for President Andrés Manuel López Obrador, who praises and relies on the army to a degree unparalleled in recent Mexican history. However, his administration has pledged to get to the bottom of the mystery and prosecute anyone responsible.

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