Investigators looking into the EgyptAir flight MS804 crash said the word “fire” was clearly audible in the black box recordings from the cockpit. However, the investigative committee said while it appeared the crew discussed the possibility of a fire on board, it remains unclear what really caused the plane to crash with 66 people on board on May 19.

The flight recorder had earlier indicated there was smoke in the cabin. Parts of the wreckage, which have been recovered from the sea in a series of operations, showed that there was damage from high temperatures and soot on the aircraft’s front end. Investigators also know that before the plane went off radar, smoke detectors had gone off in a toilet.

Officials have not been able to determine whether the plane came down by accident or was attacked by terrorists. The vessel that was conducting deep sea search operations, The John Lethbridge, has finished looking for human remains, the BBC reported. The remains found earlier have been sent to Cairo, where they will be identified.