At least 33 people arrested on suspicion of illegal mining are found dead while in Nigerian security custody, according to multiple reports. Officials say the deaths are being investigated to determine what caused them.

The outlets describe detainees held in custody conditions that may have contributed to health complications. One report says 65 detainees are packed into a poorly ventilated cell, and officials suspect disease and/or other medical factors. Another account notes that the precise cause of death is not yet confirmed.

Bodies have been sent to a local hospital for further medical examination to establish the actual cause of death. While officials point to disease as a likely factor, the reports also raise the possibility that overcrowding and inadequate ventilation may play a role. Investigators continue to assess the circumstances in custody and the timeline of the deaths.