MEXICO CITY (AP) — The authorities have found the remains of 167 people in a cave in southern Mexico, and forensic experts believe the bodies are at least 50 years old, according to a statement released Saturday by prosecutors in Chiapas State.

The prosecutors said the remains were found Friday on the Nuevo Ojo de Agua ranch, in an area frequently used by Central American migrants traveling north. They said that the remains, which “break easily,” bore no visible signs of violence.

The statement said the authorities would “not discard any line of investigation.”

The remains were discovered stacked atop one other in the cave, said a prosecutor’s office employee, who was not authorized to release information and asked not to be identified. They were moved to the state capital of Tuxtla Gutiérrez for examination, the employee said.

In the last two years, mass graves containing the bodies of dozens of migrants and others believed to have been killed by drug gang members have been found, mainly in northern Mexico.