Andreas Lubitz, the Germanwings co-pilot believed to have crashed his jet into the French Alps on purpose, apparently hid an illness from his employer, investigators said on Friday.
In searches of the co-pilot's homes, investigators found torn-up doctor's notes, including one excusing him from work on the day of the crash, prosecutors in Dusseldorf said.
Investigators did not elaborate on the illness or say whether it was mental or physical. The searches also did not turn up a claim of responsibility, a goodbye note or a suggestion of political or religious motive, prosecutor Ralf Herrenbrueck said.
Paperwork related to Lubitz's medical treatment "will take a few days," he said. But the torn-up notes support the assumption "that the deceased concealed his illness from his employer as well as his work environment," he said.
Herrenbrueck's office later told NBC News that one of the notes — doctor's statements that declared Lubitz unfit for work for several days — applied to Tuesday, the day of the crash.
"It seems clear that he deliberately ignored the doctor's directive," a spokesperson said.
On Thursday, French investigators said they had concluded that Lubitz locked the pilot out of the cockpit and used the autopilot to crash the plane, Germanwings Flight 9525 from Barcelona to Dusseldorf. All 150 people on board were killed.
Germanwings said on Friday that it never got a sick note for the day of the crash.
A Dusseldorf hospital said that Lubitz was seen there in February and most recently on March 10, but it said that reports that he was being treated there for depression were inaccurate. The hospital declined to elaborate, citing patient confidentiality.
The revelations came after teams emerged late Thursday from Lubitz's parents' home in Montabaur — some 40 miles northwest of Frankfurt — carrying blue bags, a big cardboard box and what looked like a large computer. Another person who came out was shielded from reporters by police, the Associated Press reported.
Investigators also searched the apartment that Lubitz kept in an upscale three-story building in an affluent neighborhood in Dusseldorf.
The focus on Lubitz arose out of revelations from French investigators that the cockpit voice recorder — recovered from the pulverized wreckage — indicated Lubitz locked his captain out of the cockpit and put the Airbus A320 into a rapid descent.
Amid questions over what could have driven Lubitz to down the Germanwings plane, German tabloid Bild reported that the pilot, whose training included a spell at a flight school in Arizona, received psychiatric treatment for a "serious depressive episode" six years ago and recently had a "severe relationship crisis." NBC News has not confirmed the report.
Carsten Spohr, chief executive of Germanwings' parent company Lufthansa, told a news conference that Lubitz had taken a break during his training six years ago — but did not explain why and said he had passed all tests to be fit to fly.
He told NBC News the airline had no plans to change safety rules to ensure another person was in the cockpit at all times, despite similar moves by other European carriers.
"I don't see any need to change our procedures," he said, stressing his "firm confidence in the selection of our pilots, in the training of our pilots, in the qualification of our pilots, in the work of our pilots."
NBC News' Katy Tur in Dusseldorf and Carlo Angerer contributed to this report, which originally appeared on NBCNews.com.