Düsseldorf prosecutor Christoph Kumpa also said that a second black box had been recovered as the probe into Andreas Lubitz's actions continues more than a week after the crash.
The officials said they had recovered a tablet from Lubitz's home that had been used between March 16 and 23, the day before the crash. Kumpa said Lubitz, 27, had also used the tablet to do research for ways to carry out suicide -- suggesting a degree of premeditation.
The Germanwings plane that departed from Barcelona crashed en route to Dusseldorf on March 24 with all 150 people on board killed on impact.
German authorities had previously said that Lubitz had also been treated by a psychotherapist because of previous suicidal tendencies and that he had deliberately flown the jetliner into a mountain.
Authorities did not find a suicide note.
Also today, French Prosecutor Brice Robin in Marseille confirmed the recovery of the black box, which was burnt. They are continuing to identify victims with the help of DNA provided by family members. The officials said they are hopeful to be able to get information from the flight data recorder despite its condition.
Robin also said they found 42 cellphones in the wreckage and that they were "very, very damaged."
Asked about the cellphone video that purported to show the final moments before the plane went down, Robin said, "I don't have any information" about it.
Germanwings CEO Olivier Wagner, speaking at a press conference in Marseille earlier this week, called the crash the "saddest day of my life. The families are always asking me, 'Why had this happen?' I cannot give them an answer."
Authorities have said Lubitz hid evidence of an illness from his employers, including a sick note that was found torn up inside his apartment in Dusseldorf dated from the day of the crash.