German prosecutors have closed their investigation into the crash of a Germanwings passenger aircraft in the French Alps nearly two years ago.

On March 24, 2015, co-pilot Andreas Lubitz locked the captain of flight 9525, from Barcelona to Dusseldorf, out off the cockpit. Lubitz then deliberately set the plane on a collision course with a mountainside, killing all 150 people on board, including himself.

During the investigation it was determined that Lubitz had long suffered from depression. He sought professional help several times, concealing it from his employer as it is widely known that he would quickly lose his pilot's license should his treatment come to light. In his diary, extracts from which were published by Bild newspaper, he wrote that he "sees the world pass him by" and that the only way out could be "jumping off a cliff."

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According to prosecutors, no fault was found on the part of Germanwings, its parent company Lufthansa, or the mental health doctors who treated Lubitz but did not inform authorities due to the strict regulations in the country regarding medical nondisclosure.

"There are certain laws that do not allow doctors to reveal information, they consider it confidential," said Robert Tansill Oliver, the father of a crash victim, in an interview with Global National.

"But the big question is: how can you invade the privacy of a dead person?"

Relatives of the passengers killed in the crash insist that Lubitz should have been more thoroughly screened. and subsequently suspended from piloting, due to his condition. More than half of the victim's families filed a lawsuit against the Airline Training Center of Arizona (ATCA) that trained Lubitz, accusing the flight school of negligence and "failing to apply to its own well-advertised 'stringent' standards to discover the history of Lubitz's severe mental illness."

The crash prompted German authorities to introduce new medical rules for pilots and boost cockpit security. Many European airlines now require that at least two people remain in the cockpit at any given time, to prevent just such an occurrence.