Pictures showed police inside a house in the German town of Montabaur, about 100 kilometers (62 miles) north-west of the city of Frankfurt. Prosecutors also said searches were being carried out further north in the city of Düsseldorf, where Tuesday's doomed flight from Barcelona was bound.
"Both the residence of the co-pilot in Düsseldorf and the residence in Montabaur have been searched," senior prosecutor Ralf Herrenbrück told AFP. Gabriele Wieland, chair of the Montabaur branch of the CDU, told Germany's DPA news agency that Lubitz lived with his parents in Montabaur and kept a flat in Düsseldorf.
French investigators believe Lubitz, 28, deliberately set the Airbus A320 on its fatal descent on Tuesday - locking himself in the cockpit and adjusting the altitude setting on the plane. This is a conclusion reached through audio recordings from one of the downed plane's black boxes.
All 150 passengers aboard the plane were killed when the plane crashed in the French Alps.
Lubitz, a German national, had worked for Germanwings - Lufthansa's budget subsidiary - since September 2013. He qualified at Lufthansa's training center and had 630 hours flying experience.
Much attention is now being focused on Lubitz's motives. 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.
"He voluntarily ... allowed the loss of altitude of the plane, which he had no reason to do. He had ... no reason to stop the pilot-in-command from coming back into the cockpit. He had no reason to refuse to answer to the air controller who was alerting him on the loss of altitude," Robin said.
The audio appears to show the captain, who left the cabin briefly, presumably to use the restroom, trying to force his way back in. "You can hear banging to try and smash the door down," Robin said, adding that screams were also heard, although passengers would not have been aware of their fate until the very end.
Robin said that prior to the captain leaving the cockpit, the conversation between the two became stilted. "His responses became very brief. There is no proper exchange as such," he said.
Happy in his job
An acquaintance of Lubitz said the young pilot seemed content in his job.
"He was happy he had the job with Germanwings and he was doing well," said Peter Rücker, a member of the local flight club where Lubitz received his flying license years ago.
"I'm just speechless. I don't have any explanation for this. Knowing Andreas, this is just inconceivable to me," Rücker said.
"He was a lot of fun, even though he was perhaps sometimes a bit quiet. He was just another boy like so many others here."
A photo taken Lubitz's Facebook page, which has since been deactivated, shows him smiling in front of San Francisco's Golden Gate bridge (seen above).
A "stunned" Lufthansa CEO Carsten Spohr said the airline's air crew were subjected to psychological testing and carefully vetted.
"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," Spohr said.
Spohr said he was "speechless that this aircraft has been deliberately crashed," describing it as the most terrible event in the company's history.
German Chancellor Angela Merkel said on Thursday the news "was purely beyond the power of imagination."
"It shocks me very deeply," she told reporters. "We don't know all of the reasons."
Germanwings captain calms passengers
DW journalist Richard Connor caught a Germanwings flight to the United Kingdom on Thursday. He was due to board the plane when the information on Lubitz started to come through.
"I certainly felt weird getting on the plane," Connor said in an email. "I kind of felt better when the captain gave an inflight announcement."
Here is what the captain said:
"Ladies and gentlemen, good afternoon from the flight deck.
"First of all, great to have you on board. As you can imagine, the whole company of Germanwings still a bit under the impression of the events from Tuesday. It's not easy for us presently to get along with all the things happening and the news just coming out today, they don’t make it better.
"Nevertheless, all our thoughts and compassion are with the victims and the relatives of the victims of course. They may have been our passengers and our colleagues.
"Nevertheless, we have to get back to a regular routine somehow, even though it’s not easy of course, but we have to work of course and you have to travel to your destination, of course so we have to manage it and we will as we have shown in the couple of decades with millions of safe flights.
"We will do it in the future as well and from our side we are ready right now and we will will depart here in a couple of seconds."
jr/kms (AFP, Reuters)