Just a week after investigators found a mass grave in Iguala, Mexico, they found four new mass graves in the same area where 43 students reportedly disappeared.

Investigators found the new set of mass graves on Thursday, but officials still have not disclosed the number of bodies they contained. Authorities have launched a widespread operation to locate the students, who went missing after an encounter with police, BBC News detailed.

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Last week, authorities discovered six shallow pits with 28 charred bodies that they have yet to identify. It would take weeks before they finish the forensic tests to identify the bodies.

The four new graves are located in the same area where they found the first mass graves, according to Federal Attorney General Jesus Murillo.

The town's mayor, Jose Luis Abarca Velasquez, his wife, and security head have all gone on leave after the students' clash with police and are still away from the public eye. Murillo said they have launched a search for the three.

So far, federal authorities have apprehended 34 people in connection with the missing students' case. Most of those arrested are local police forces.

The clash happened on September 27 while the students were protesting the hiring practices of the government. They were last seen being hauled into several vehicles, the report said.

People have constructed different theories for their disappearance; with some saying they may have fuelled the ire of Guerreros Unidos, a drug gang in the town, by not paying extortion fees. Others think it is connected with the speech that Mrs. Velasquez gave on that fateful day.

The mayor's wife was talking to dignitaries in Iguala and some people think the students were picked up because they could disturb the event.

While the missing students all had backgrounds in left-wing activism, it is yet to be confirmed if their political beliefs had something to do with the clash and their disappearance.

TagsMexico, Mass grave, Iguala, Jose Luis Abarca Velasquez, education