An investigator into the Germanwings plane crash found that one pilot who left the cockpit before the plane’s descent was locked out before the crash following the analysis of the cockpit voice recorder.

A senior military official involved in the investigation described a calm conversation between the pilots during the start of the flight from Barcelona, Spain, to Dusseldorf, Germany, until one of the pilots left the cockpit. When he returned, he knocked on the door but there was no answer. He kept knocking, louder this time, but there was no answer. The audio indicates that the pilot outside consequently tried to smash the door down.

It is still unknown why the other pilot inside did not open the door. The data from the voice recorder shows that the twin-engine Airbus A320 appeared undamaged as it began to descend gradually. Its drop was slow from 38,000 feet, taking about 10 minutes before it slammed into the craggy mountainside, scattering debris over a wide area and killing everybody on board upon impact.

The mystery as to why the pilots did not communicate with air traffic controllers is being investigated. It is possible that the plane’s automated system may have been trying to maintain control of the plane as it dropped. Various theories are being investigated. It is possible that the pilot in the cockpit may have been incapacitated by a sudden event such as a drop in cabin pressure or fire.

This information has yet to be officially confirmed. A press conference will be given once all information is analysed.

The plane’s other black box was found at the site of the crash but the memory card containing data on the plane’s altitude, speed, location and condition was not inside and appeared to have been either thrown loose or destroyed by the impact.