The co-pilot of the crashed Germanwings plane, Andreas Lubitz, had received treatment for suicidal tendencies before getting hispilot licence, investigators say, but not recently.
Lubitz, 27, is suspected of deliberately crashing the plane in the Alps, killing all 150 people on board.
Officials in Duesseldorf said the investigation to this point had revealed no clue to any motive.
So far, DNA strands of 80 of the victims have been found.
Duesseldorf public prosecutor Christoph Kumpa said that "several years" before Lubitz became a pilot he "had at that time been in treatment of a psychotherapist because of what is documented as being suicidal".
However, he said that since Lubitz received his licence, documentation had shown no such treatment.
"In the following period, and until recently, further doctor's visits took place, resulting in sick notes without any suicidal tendencies or aggression against others being recorded," Mr Kumpa said.
He added: "There still is no evidence that the co-pilot said beforehand that he would do what we have to assume was done and we haven't found a letter or anything like that that contains a confession.
Mr Kumpa said: "We have not found anything in his surrounding [environment] - be it personal or his family or his professional surrounding - that is giving us any hints that enable us to say anything about his motivation."
There had been some media reports that Lubitz had problems with his vision, possibly a detached retina.
But Mr Kumpa said there was no documentation on any sight problems that were caused by an "organic illness".
There has also been widespread speculation about Lubitz's romantic life.
While one unconfirmed report has suggested his long-term girlfriend was pregnant, an ex-girlfriend has revealed that he vowed last year to do something memorable.
"One day I'm going to do something that will change the whole system, and everyone will know my name and remember," she quoted him as saying.