03/26/2015 09:39 EDT | Updated 05/26/2015 05:59 EDT

Andreas Lubitz, Germanwings Flight 4U9525 co-pilot, called '100% fit to fly'

Andreas Lubitz, the Germanwings co-pilot who authorities say deliberately crashed a plane with 150 people on board in the French Alps Tuesday, was "rather quiet" and showed no overt signs of his intentions, people who know him said Thursday.

The 28-year-old German citizen wasn't known to authorities and had no obvious connections to terrorist groups, French prosecutor Brice Robin told a news conference this morning. Robin did not comment on Lubitz's religious leanings or ethnic background, saying that German authorities have taken over the investigation into the co-pilot.

Lubitz had been with Germanwings since September 2013 and had logged 630 flight hours. He trained at the airline's flight centre in Bremen, Germany, and at a related facility in Phoenix, Ariz., Lufthansa CEO Carsten Spohr told a media briefing this morning.

- LIVE BLOG | Germanwings crash

Lubitz began his training process with Lufthansa in 2008, though that process was briefly "interrupted" for several months, Carsten said. He could not elaborate on the reasons for the break. 

After completing the training process, Lubitz worked as a flight attendant with the airline as he waited for an opportunity to fly as a junior co-pilot, Carsten said. 

"He passed all medical exams, all checks," Carsten said. "He was 100 per cent fit to fly without any restrictions."

Carsten told reporters that while Lufthansa requires all pilots to undergo a medical exam each year, those tests do not necessarily include psychological elements.

Shortly before the crash, Lubitz had engaged in "very smooth, very cool" conversation with the pilot, authorities said, citing audio recordings of the cockpit. 

Lubitz deliberately sent the Airbus A320 into a descent after locking the armoured cockpit door when the pilot left to use the bathroom, Robin said.

He did not respond to repeated calls from air traffic control in Marseilles or from the pilot trying to re-enter the cockpit, but could be heard breathing calmly on the audio recording before the airliner smashed into a remote French mountain. 

According to acquaintances in Germany, Lubitz "gave off a good feeling" when he recently renewed his glider pilot's licence in the town of Montabaur. 

"He was happy he had the job with Germanwings, and he was doing well," said Peter Ruecker, a member of the glider club who watched him learn to fly.

Lubitz had obtained his glider pilot's licence as a teenager, and was accepted as a Lufthansa pilot trainee after finishing a tough German college preparatory school, Ruecker said.

He described Lubitz as a "rather quiet" but friendly young man.

In a statement issued before authorities revealed his role in the crash and since taken down, the LSC Westerwald Flight Club — of which Lubitz was a member — said he had joined the club in his youth "to fulfill his dream of flying."

On mobile? Explore the live blog here