MEXICO CITY (AP) — Investigators in the northern Mexico border state of Nuevo León said Thursday they have found at least five burned bodies in a vehicle on a roadway near the industrial hub of Monterrey.

State prosecutors said they initially found a body and some skulls inside a burned-out vehicle in the township of Pesqueria, just outside Monterrey. The area where they were found may have been used as a body dumping ground previously.

Later they found other bodies, human bones and more skulls nearby. While there were five bodies and five skulls, it was not clear if they belonged to each other. Investigations were underway to determine exactly how many victims there were, and how they died.

In the early 2000s, Monterrey was ravaged by violence from the old Zetas cartel, but had become calmer. A splinter group of that cartel, the Cartel of the Northeast, remains in control of the border city of Nuevo Laredo, in the neighboring state of Tamaulipas.