Air crash investigators examining a computer belonging to Germanwings co-pilot Andreas Lubitz are trying to determine whether the killer 'spiked' his captain's drink to force him into the toilet. Lubitz, 27, crashed the Airbus A320 passenger jet into the Alps changing the aircraft's altitude to just 100 feet using the autopilot, sending it on collision course with the Alps. German prosecutors believe that Lubitz may have added a chemical to Captain Patrick Sodenheimer's coffee to remove him from the flight deck. Scroll down for video . Andreas Lubitz may have spiked his Captain's coffee so he would be left alone on the aircraft's flight deck . Investigators have been scouring Lubitz's computers to determine his state of mind before the tragedy . Lubitz remained silent during the final eight minutes of the flight as it flew into the Alps . Once Captain Sodenheimer closed the cockpit door, Lubitz enabled special security features preventing the reinforced door from reopening. The safety systems were introduced following the 9/11 attacks although the designers did not consider a rogue pilot seeking to kill himself while taking his passengers and fellow crew with him. Already it has emerged that Lubitz used his computer to research methods of killing himself as well as information concerning the cockpit door locking mechanism. It is understood that European safety chiefs had concerns about Germanwings' safety procedures in the weeks before the crash. In November 2014, the European Commission contacted several airlines and 'had asked for clarification to make sure all airlines actively observe rules'. Following the crash, it emerged that Lubtiz suffered from crippling depression although Lufthansa, who own Germanwings, did not pass on this information to aviation regulators. Investigators believe that Lubitz, 27, informed its flight school when he returned from a several-month break in pilot training in 2009 that he had experienced an episode of 'severe depression'. Lufthansa has said he subsequently passed all medical tests. The EU has detailed air safety regulations, which included rules on a pilot's mental health, that member states need to take into account. EASA regularly tests whether the 28 EU nations adhere to those standards. 'This is a normal and regular occurrence,' said the official.
Investigators have been searching Andreas Lubtiz's internet search history . Lubitz sought information online on various methods of taking his own life . He is also believed to have researched the cockpit door locking system . Investigators now want to determine why the captain left the cockpit .