An animation has been produced that shows what could have happened between the two pilots in the downed Germanwings 9525 flight.
A young German co-pilot barricaded himself alone in the cockpit of Germanwings flight 9525 and apparently set it on course to crash into an Alpine mountain, killing all 150 people on board including himself, French prosecutors said on 26 March.
They offered no motive for why Andreas Lubitz, 27, would take the controls of the Airbus A320, lock the captain out of the cockpit and deliberately set it veering down from cruising altitude at 3,000ft per minute.
German police searched his home for evidence that might offer some explanation for what was behind 24 March crash in the French Alps.
The scenario stunned the aviation world. Within hours of the prosecutors' announcement, several airlines responded by immediately changing their rules to require a second crew member to be in the cockpit at all times. That is already compulsory in the United States but not in Europe.
Cockpit doors can be opened from the outside with a code, in line with regulations introduced after the 11 September 2001 attacks in the United States, but the code can be overridden from inside the cockpit, making the door impenetrable.