CNN CNN International May 7, 2015 07:10:00
Neither air traffic control nor the captain noticed irl ed irregularities in the plane's flight. they believe that's because it was in the process of descending when lubitz played with the controls. the captain didn't notice anything because the action by the co-pilot during the outbound flight was made during a normal programmed descent, so it didn't have any impact on the plane's trajecto trajectory. lubitz crashed the jet on the next flight. german police discovered he researched suicide methods and the locking mechanism of the cockpit door on line. the interim hort also air traffic control...
Source: archive.org