French prosecutors have yet to offer a motive for why Lubitz, 28, took the controls of the Airbus A320, locked the captain out of the cockpit and deliberately set it veering down from cruising altitude at 3,000 feet per minute.
French and German officials said there was no indication he was a terrorist. Acquaintances of Lubitz told Reuters he was as an affable young man who had given no sign of harboring harmful intent.
According to Marseille prosecutor Brice Robin, Lubitz acted "for a reason we cannot fathom right now, but which looks like intent to destroy this aircraft,” adding that “suicide” was the wrong word to describe the actions that killed so many other people.
"I don't necessarily call it suicide when you have responsibility for 100 or so lives," Robin said.
The aircraft's first black box, the cockpit voice recorder, was recovered on Tuesday, while parts of the second black box, the flight data recorder, was found a day later.
Judging by the sound recordings from one of the black boxes, Robin said most of the passengers would not have been aware of their fate until the very end.
"I don't necessarily call it suicide when you have responsibility for 100 or so lives." — French prosecutor Brice Robin
"Only toward the end do you hear screams," he said. "And bear in mind that death would have been instantaneous… the aircraft was literally smashed to bits."
The CEO of Lufthansa, parent company of Germanwings, said its air crew were picked carefully and subjected to psychological vetting.
"No matter your safety regulations, no matter how high you set the bar, and we have incredibly high standards, there is no way to rule out such an event," CEO Carsten Spohr said.
Attention will now focus on Lubitz, a German national who joined Germanwings in September 2013 and had just 630 hours of flying time – compared with the 6,000 hours of the flight captain, named in German media only as "Patrick S."
Police set up guard outside Lubitz's house in Montabaur, Germany. Acquaintances in the town told Reuters they were stunned.
"I'm just speechless. I don't have any explanation for this. Knowing Andreas, this is just inconceivable for me," said Peter Ruecker, a long-time member of the local flight club where Lubitz received his flying license years ago.
Robin, the French prosecutor, said there was nothing alarming about the conversation between the two pilots, but that Lubitz's replies became brief as they started readying for the planned descent to the airport in Duesseldorf.
