Investigators: Germanwings Co-Pilot Treated for Suicidal Thoughts Years Ago

Investigators say they have yet to find a motive in the downing of Germanwings flight 4U 9525 over the French Alps last Tuesday.

Prosecutors investigating the case say that after searching co-pilot Andreas Lubitz's home and medical records, they discovered that the 27-year-old had been treated for suicidal tendencies years ago, but reportedly showed no threat to the crew or passengers when he flew on March 24.

Lubitz had also reportedly received sick leave notes from physicians for an undisclosed illness which he failed to show to his employee, Germanwings Airlines, which is owned by Lufthansa Airlines.

"At no point ever did we know he was sick," Lufthansa spokesman Wolfgang Weber told USA TODAY. "The captain was also 100% fit. We would never let anyone fly if they weren't. We can't. If a pilot is sick in any way, they have no valid license."

According to ABC News, investigators in Germany have started a special investigative group to find details on Lubitz's life that may have led to a motive for last week's crash that killed all 150 passengers and crew on board. The special investigation team has also been assigned to collect information on the 70 Germans killed in the plane crash.

Germanwings CEO Olivier Wagner recently described last week's crash as "the saddest day of my life. The families are always asking me, 'Why had this happen?' I cannot give them an answer."

Investigators have reiterated their claim that regardless of Lubitz's past psychological treatment for suicidal tendencies, there is no evidence to suggest that he posed a threat to others on the day of the crash.