Debris from crashed EgyptAir Flight MS804 has indicated that there was smoke in the bathroom and onboard equipment, Egyptian investigators said Wednesday. The Cairo-bound flight went down in the Mediterranean Sea in May killing all 66 people aboard.

The investigators said that the wreckage from the plane’s front section showed “signs of high temperature.” A flight data recorder suggested that there was smoke on the doomed Airbus A320.

“Analysis will be carried out to try and identify the source and reasons for those signs,” the investigators said in a statement.

The data was recovered from one of the plane’s black boxes. The second black box, a damaged cockpit recorder, has been sent to Paris for repair. The debris was located earlier this month.

During initial investigation, radar data showed that MS804 did not suffer a sudden midair explosion. However, electronic messages sent by the plane indicated some smoke alarms went off.

Luggage and body parts have been found some 180 miles from the Egyptian port city of Alexandria. Investigators said that the plane, en route from Paris to Cairo, veered left off course at about 37,000 feet and made a sharp right turn and completed a full circle.

Black boxes provide investigators with important data, including the pilots’ transmissions, information about the working of plane’s engines, navigation systems, and auto-pilot working and smoke alarms. It remains unclear what led to the crash of MS804, but terrorism has not been ruled out.

French authorities reportedly launched a manslaughter inquiry into the incident Monday. However, the officials said that no evidence so far has linked the crash to terrorism.