Theories behind riddle of Germanwings co-pilot's actions in Alps crash

BERLIN (AFP) - The crash of Germanwings Flight 4U 9525 has sparked a range of possible theories to explain the actions of co-pilot Andreas Lubitz, who investigators believe deliberately flew the plane into a mountainside.

Reports have focused on the health of the 27-year-old and whether it played a role in what seems to have been both an act of suicide and mass murder of another 149 people.

Mental health experts caution that suicide is usually the result of multiple, complex factors and warn against overly simplistic explanations.

Here are some of the different theories:

Mental Health Problems?

- German media reports have said Lubitz was suffering from serious depression but these have not been confirmed. German prosecutors on Friday said medical documents had been found at Lubitz's homes suggesting "existing illness and appropriate medical treatment" but they did not specify the ailment. They also revealed that torn-up sick leave notes had been discovered, including for the day of the crash, and that evidence backed up suspicions he hid an illness from his airline.

According to Germany's Welt am Sonntag newspaper, medical treatments for psychological illness were found at his Duesseldorf home.

French and German investigators declined to confirm or deny the report.

Bild daily reported Friday that Lubitz sought psychiatric help for "a bout of serious depression" in 2009 and was still getting assistance from doctors, quoting documents from Germany's air transport regulator.

Duesseldorf University Clinic later said that Lubitz had received diagnostic care in February and March but denied it was treatment for depression.

Lufthansa CEO Carsten Spohr has said that Lubitz suspended his pilot training, which began in 2008, "for a certain period", before restarting and qualifying in 2013 but gave no further details.

Relationship crisis?

- Bild on Friday also cited security sources as saying that Lubitz and his girlfriend were having a "serious crisis in their relationship", which is also unconfirmed.

- Sunday's Bild reported, without giving its sources, that his girlfriend with whom he lived in Duesseldorf was believed to be pregnant. There has been no confirmation.

- French investigator Jean-Pierre Michel said on Saturday that the investigation so far has not turned up a "particular element" in the life of the co-pilot which could explain his alleged action.

Sight problems?

- Reports in the New York Times and Sunday's Bild say Lubitz sought treatment for a vision problem and that it was not clear if it was psychosomatic. Bild said it was believed to be retinal detachment. These reports are unconfirmed.

Fearful his licence wouldn't be renewed?

- Bild newspaper said on Saturday that Lubitz's flying licence was up for renewal in June - which has not been confirmed - and questioned whether he feared it not being extended.

Seeking notoriety?

- Bild on Saturday also quoted an unidentified flight attendant who, it said, had had a relationship with Lubitz last year, as saying he had indicated he wanted to go down in history.

"One day I'm going to do something that will change the whole system, and everyone will know my name and remember," she recalled him having said.

Duesseldorf prosecutors said on Friday they had not found a suicide note, confession or anything pointing to a "political or religious" motive.