Federal agents have been implicated in one of Mexico's most notorious and unsolved crimes

Two Mexican federal police officers allegedly participated in the disappearance of 43 students from a rural teachers' college in the southwest state of Guerrero in September 2014, the National Human Rights Commission said Thursday, implicating national agents in the case for the first time.

Citing an unidentified witness, the governmental rights body said the federal agents were involved with municipal officers in the disappearance of a group of teacher trainees in the southern city of Iguala.

Prosecutors have already charged municipal police officers in connection with the mass abduction in the southern city of Iguala on September 26-27, 2014.

But the governmental rights commission said it found an eyewitness who saw two federal agents near Iguala's courthouse, where municipal officers had stopped a bus with 15 to 20 students on board.

The commission also said another local police department, from the town of Huitzuco, had a previously unknown role in the disappearance, which occured after the students seized buses that were meant to take them to Mexico City to participate in a protest.

Municipal police in Iguala fired on the buses, forcing them to stop, after which the students threw rocks at the officers.

The officers bundled the students into several patrol vehicles, including three from Huitzuco. When the federal officers arrived, they asked what was going on.

An Iguala officer said the students would be sent to Huitzuco, where "the boss" - possibly a drug cartel member - 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.

Huitzuco would be a new location in the twisting saga, as authorities have maintained that suspects told investigators that the students were killed in the nearby town of Cocula.

The commission said there was enough evidence to "presume the participation of members of the Huitzuco municipal police and two federal police officers" in the disappearance, adding that it has the name of one of the two federal agents, which it gave to prosecutors.

The commission also said a soldier on a motorcycle took pictures of the incident and then left. Families of the victims have called for an investigation into whether the military had a role in the case, but the army denies any wrongdoing.