BERLIN - The co-pilot of Germanwings Flight 9525 appears to have researched suicide methods and cockpit door security in the days before he crashed the plane into the French Alps, killing everyone aboard, German prosecutors said Thursday.

Search terms found on a tablet computer at co-pilot Andreas Lubitz's apartment in Duesseldorf provided the first evidence that his actions may have been premeditated.

After listening to the cockpit voice recorder, investigators believe Lubitz, 27, locked his captain out of the Airbus A320 cockpit on March 24 and deliberately sent the plane into a French mountain, killing all 150 passengers and crew.

Investigators said Thursday they had reviewed search terms from March 16-23 that were found on the browser memory of Lubitz's computer, which hadn't been erased.

The co-pilot "informed himself about types and ways of going about a suicide," Duesseldorf prosecutors' spokesman Ralf Herrenbrueck said in a statement. "In addition, on at least one day, (Lubitz) concerned himself for several minutes with search terms about cockpit doors and their security precautions."

Prosecutors didn't specify which day that was and said they wouldn't disclose the individual search terms that Lubitz used. They said personal correspondence and search terms on the tablet "support the conclusion that the machine was used by the co-pilot in the relevant period."

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French prosecutors, meanwhile, announced that the jet's second black box had been found — the data recorder, which captures 25 hours of information on the position and condition of nearly every part of the plane.

The data recorder was "completely blackened" as though it had been burned and had been buried on a ravine "already explored several times," Marseille Prosecutor Brice Robin said, adding that it may still be usable.

He said investigators had identified body parts from all 150 people aboard the Germanwings flight after finding and studying 2,854 pieces of remains. But he added it will still take a long time for investigators to match the body parts with DNA samples from families of the victims.

At least 40 cellphones have been found at the crash site in "very, very damaged" condition, Robin said.

No video or audio from the cellphones of those aboard the plane has been released publicly. But a French reporter who says he saw video from one cellphone described the excruciating sound of "screaming and screaming" as the plane flew full-speed into the mountain.

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Questions persist about journalist Frederic Helbert's reports in the French magazine Paris-Match and in the German tabloid Bild this week about the video that he says he saw, but Helbert vigorously defended his reports in an interview Thursday with The Associated Press.

Helbert said he viewed the video thanks to an intermediary close to the crash investigation, but does not have a copy of it himself. It was shot from the back of the plane, he said, so "you cannot see their faces, but you can hear them screaming and screaming."

"No one is moving or getting up," he told the AP in Paris. "People understand something terrible is going to happen."

Germanwings, meanwhile, said Thursday it had been unaware that Lubitz had suffered from depression during his pilot training.

Lufthansa, Germanwings' parent company, confirmed Tuesday that it knew six years ago that Lubitz had suffered from an episode of "severe depression" before he finished his flight training. Germanwings hired Lubitz in September 2013.

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German prosecutors have said Lubitz's medical records from before he received his pilot's license referred to "suicidal tendencies," but visits to doctors since then showed no record of any suicidal tendencies or aggression against others.

Investigators also have found torn-up sick notes from doctors at Lubitz's home, including one that would have kept him off work on the day of the crash.

Germany also announced the creation of an expert task force to examine what went wrong in the Germanwings crash and consider whether changes are needed regarding cockpit doors, how pilots pass medicals and how companies recognize psychological problems in employees. Any conclusions will be shared with international air safety organizations.

France's air accident investigation agency is already examining cockpit entry and psychological screening procedures after the crash.