The commission announced Thursday it had found an eyewitness who alleges federal officers were present at the scene of the abduction in Mexico's southwestern Guerrero state.

Jose Larrieta Carrasco, the commission member investigating the case, said the new evidence suggested the officers did nothing to stop local police from taking the youths away.

The 43 student teachers disappeared in the city of Iguala on September 26, 2014. Investigators say local police from Iguala and the town of Cocula picked the students up and turned them over to the Guerreros Unidos drug cartel, who allegedly killed them and incinerated their bodies.

In a new development, the unnamed witness said members of a third town's police force, Huitzuco, had also participated, the commission said.

"The facts released today could constitute clear evidence of the coopting of municipal institutions by criminal organizations in Iguala, Cocula and, now with the information being released, probably Huitzuco," Larrieta said. "In the same way it could be an example of the alleged involvement of federal police officers."

To date, the remains of only one of the students has been positively identified by burned bone fragments found near a local dump.

Witness report

According to the new witness, the two federal officers intervened at one point and asked local police what they were doing with the students. Iguala officers reportedly told them they would be taken to "the boss," who would "decide what to do with them," the commission said.

The federal officers responded, "Ah, OK, that's good," and allowed the local police to take the students away.

Larrieta Carrasco said the federal officers involved should be investigated. He added that the probe should also include a number of private companies, suspected of being in the cartel's pocket, who had failed to cooperate with the investigation.

"Representatives of the companies involved have hidden information, or may have covered up for those responsible for these acts," Larrieta said, without specifying which firms he was referring to.

The Attorney General's office said it had put the witness under protection and pledged to follow up on this "line of investigation."

Rights groups and independent investigators have criticized the Mexican government's probe into the students' disappearance. The case has sparked huge protests in Mexico and led to a significant drop in President Enrique Pena Nieto's approval rating. German Chancellor Angela Merkel this week offered Mexico help with its investigation into the students' fate.

nm/cmk (AP, AFP)