The Germanwings co-pilot reportedly received psychiatric treatment for a 'serious depressive episode' several years ago

The pilot who appears to have deliberately crashed a plane carrying 149 others into the French Alps received psychiatric treatment for a "serious depressive episode" six years ago, German tabloid Bild reported on Friday.

Prosecutors in France, after listening to the cockpit voice recorders, offered no motive for why Andreas Lubitz, 27, would take the controls of the Airbus A320, lock the captain out of the cockpit and deliberately set it veering down from cruising altitude at 3,000 feet per minute.

Citing internal documents and Lufthansa sources, Bild said Lubitz spent a total of one and a half years in psychiatric treatment and that the relevant documents would be passed to French investigators once they had been examined by German authorities.

Lufthansa Chief Executive Carsten Spohr told a news conference on Thursday 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.

"Six years ago there was a lengthy interruption in his training. After he was cleared again, he resumed training. He passed all the subsequent tests and checks with flying colors. His flying abilities were flawless," Spohr said.

A Lufthansa spokeswoman said on Friday the airline would not comment on the state of health of the pilot.

Marseille public prosecutor Brice Robin said at a press conference on Thursday that this week's plane crash "was not an accident" and that it was Lubitz's "intention to destroy this plane."

On the cockpit voice recording recovered from the crash site, Lubitz could reportedly be heard breathing from when the captain left the cockpit until the plane crashed, but he did not say a word. The captain was reportedly banging on the cockpit door and trying to break it down, but Lubitz would not open the door.

French authorities contend that Lubitz input the command to start the plane's descent after the captain left the cockpit.

"It's obvious this co-pilot took advantage of the commander's absence," Robin said. "Could he have known he would leave? It is too early to say."

Some pilots, however, have been shocked by authorities' allegations that Lubitz intentionally crashed the plane.

James Phillips, international affairs director of the German Pilots Association, told Time: "It is a very, very incomplete picture. ... I have the feeling that there was a search for a quick answer, rather than a good answer."

Those who knew Lubitz also seemed shocked at the news that he apparently crashed the passenger plane intentionally. People close to him described him as "rather quiet," "polite," and "fun."

"He had a lot of friends, he wasn't a loner," Peter Ruecker, a member of the LSC flight club and good friend of Lubitz, told Reuters. "Knowing Andreas, this is just inconceivable for me. ... He was very happy he had the job with Germanwings and he was doing well."

Lubitz joined Germanwings in September 2013 after training at the Lufthansa Flight Training School in Bremen, according to Lufthansa officials. He had little professional flight experience, having only logged 630 flight hours before co-piloting the doomed flight 9525.

Officials have not offered a motive for the crash.

(Reporting by Victoria Bryan; editing by John Stonestreet)