As German prosecutors sought to piece together the puzzle of why Lubitz locked his captain out of the cockpit and crashed the Airbus A320, police in the French Alps toiled to retrieve the shattered remains of the 150 people killed in Tuesday's crash.
Searches conducted at Lubitz's homes in Duesseldorf and in the town of Montabaur turned up documents pointing to "an existing illness and appropriate medical treatment," but no suicide note was found, said Ralf Herrenbrueck, a spokesman for the Duesseldorf prosecutors' office.
They included ripped-up sick notes covering the day of the crash, which "support the current preliminary assessment that the deceased hid his illness from his employer and colleagues," Herrenbrueck said in a statement.
Doctors commonly issue employees in Germany with such notes excusing them from work, even for minor illnesses, and workers hand them to their employers. Doctors are obliged to abide by medical secrecy unless their patient explicitly tells them he or she plans to commit an act of violence.
Prosecutors didn't specify what illness Lubitz may have been suffering from, or say whether it was mental or physical. German media reported Friday that the 27-year-old had suffered from depression.
The Duesseldorf University Hospital said Friday that Lubitz had been a patient there over the past two months and last went in for a "diagnostic evaluation" on March 10. It declined to provide details, citing medical confidentiality, but denied reports it had treated Lubitz for depression.
Neighbours described a man whose physical health was superb and road race records show Lubitz took part in several long-distance runs.
"He definitely did not smoke. He really took care of himself. He always went jogging. ... He was very healthy," said Johannes Rossmann, who lives a few doors from Lubitz's home in Montabaur.
People in Montabaur who knew Lubitz told The Associated Press that he had been thrilled with his job at Germanwings and seemed very happy.
On Friday, no one was seen coming or going from his family's large slate-roofed two-story house in Montabaur as more than 100 journalists remained outside. Mayor Edmund Schaaf appealed to the media to show "consideration."
"Independent of whether the accusations against the co-pilot are true or not, we have sympathy for his family," he said.
Germanwings said that both pilots on the plane had medical clearance, and it had received no sick note for the day of the crash. Medical checkups are done by certified doctors and take place once a year.
A German aviation official told the AP that Lubitz's file at the country's Federal Aviation Office contained a notation that meant he needed "specific regular medical examination." Such a notation could refer to either a physical or mental condition but the official, who spoke on condition of anonymity because he was not authorized to release the information, said Lubitz's file did not specify which.
German media have painted a picture of a man with a history of depression who had received psychological treatment, and who may have been set off by a falling-out with his girlfriend. Duesseldorf prosecutors, who are leading the German side of the probe, refused to comment on the anonymously sourced reports.
The U.S. Federal Aviation Administration had issued Lubitz a third-class medical certificate. In order to obtain such a certificate, a pilot must be cleared of psychological problems including psychosis, bipolar disorder and personality disorders.
The certificate also means that he wasn't found to be suffering from another mental health condition that "makes the person unable to safely perform the duties or exercise the privileges" of a pilot's license.
Carsten Spohr, the CEO of Germanwings' parent company, Lufthansa, has said there was a "several-month" gap in Lubitz's training six years ago, but didn't elaborate. Following the disruption, he said, Lubitz "not only passed all medical tests but also his flight training, all flying tests and checks."
Prosecutors said there was no indication of any political or religious motivation for Lubitz's actions on the Barcelona-Duesseldorf flight.
In the French Alps, police working to recover remains from the crash site said they so far have recovered between 400 and 600 pieces of remains from the victims.
Col. Patrick Touron of the gendarme service said DNA samples have been taken from objects provided by victims' families, such as combs or toothbrushes, that could help identify them. Jewelry and other objects could also help in the identification process, he said.
"We haven't found a single body intact," he said.
The rough terrain means that recovery workers have to be backed up by mountain rescuers. "We have particularly difficult conditions, and each person needs to be roped up," Touron said.
Also Friday, the European Aviation Safety Agency recommended that airlines in the future always have two people in the cockpit. The move came after several airlines, including Germanwings parent Lufthansa, pledged to impose the measure.
Geir Moulson reported from Berlin. Associated Press writers Frank Jordans and David Rising in Berlin, Joan Lowy in Washington and Thomas Adamson in Paris contributed to this report.
Also on HuffPost