The co-pilot suspected of deliberately crashing a Germanwings airliner into the French Alps hid details of an illness, German prosecutors say.
Torn-up sick notes were found in the homes of Andreas Lubitz, they say, including one for the day of the crash, which killed 150 passengers and crew.
A German hospital confirmed he had been a patient recently but denied reports he had been treated for depression.
The EU's aviation regulator has urged airlines to adopt new safety rules.
The European Aviation Safety Agency (EASA) said in future two crew members should be present in the cockpit at all times.
Data from the voice recorder suggests Mr Lubitz purposely started an eight-minute descent into the mountains after locking the pilot out of the flight deck.
There were no survivors when Flight 4U 9525 crashed in a remote mountain valley on Tuesday while en route from Barcelona in Spain to Duesseldorf in Germany.
Prosecutors say there was no evidence of a political or religious motive for his actions and no suicide note has been found.
In a statement (in German), prosecutors said they had seized medical documents from Mr Lubitz's two residences - his Duesseldorf flat and his parents' home north of Frankfurt - which indicated an "existing illness and appropriate medical treatment".
The "fact that, among the documents found, there were sick notes - torn-up, current and for the day of the crash - leads to the provisional assessment that the deceased was hiding his illness from his employer", the report states.
Germanwings confirmed it had not been given a sick note for the day of the crash.
Duesseldorf's University Hospital issued a statement (in German) saying Mr Lubitz had attended the hospital on 10 March and last month.
Adding that it had handed his medical records over to prosecutors, it said reports the co-pilot had been treated there for depression were incorrect.
Germany's Rheinischer Post newspaper, which spoke to the hospital, quoted its own unnamed sources as saying Mr Lubitz had been suffering from a physical, rather than a mental, illness.
French police say the search for passenger remains and debris on the mountain slopes could take another two weeks.
The theory that a mental illness such as depression had affected the co-pilot was suggested by German media, quoting internal aviation authority documents.
They said he had suffered a serious depressive episode while training in 2009.
He reportedly went on to receive treatment for a year and a half and was recommended regular psychological assessment.
Mr Lubitz's employers insisted that he had only been allowed to resume training after his suitability was "re-established".
'Rule of two'
Speaking just before the EASA issued its advice, Lufthansa announced it would adopt the "rule of two" as soon as possible.
Family members of some of the passengers and crew who died have visited Seyne-les-Alpes, near the crash site.
DNA samples are being provided to allow for identification of victims' remains.
The plane's second "black box", which records flight data, has yet to be found.
"There's not much plane debris left," police spokesman Xavier Vialenc was quoted by AFP news agency as saying. "There's mainly a lot of body parts to pick up."