CNN  — 

Details continue to emerge about the final moments of Germanwings Flight 9525 and the life of the co-pilot who authorities say appears to have set it on a fatal trajectory into the French Alps.

But the crucial question of why he would choose to crash a plane with 150 people on board remains a daunting puzzle.

Search teams are recovering remains from the mountainside where the aircraft went down, and investigators in Germany are hunting for clues.

Here’s the key information that’s available so far, and the big questions still in need of answers:

The co-pilot

Attention has focused on the 27-year-old co-pilot, Andreas Lubitz, since a French prosecutor said last week that he appeared to have locked the pilot out of the cockpit and deliberately crashed the plane.

News reports have emerged suggesting Lubitz may have been suffering from mental health problems. Antidepressants were reportedly found at his apartment in Dusseldorf, Germany.

Lubitz had visited an eye doctor because of vision problems, a European government official familiar with the investigation told CNN.

The pilot complained he was not seeing as he should, but the doctor told him the cause was psychosomatic, the official said. In part because of this, the doctor deemed Lubitz unfit for flying.

Lubitz told a different doctor – a neuropsychologist – that he was too stressed with work, the European official said.

The dates of these visits are unclear, but they could have been earlier this year.

The official said he is not aware of any suicidal tendencies reported by Lubitz to the doctors, but that investigators believe he was suicidal.

Officials say Lubitz had been hiding an illness from his employer. Authorities said investigators found torn-up medical leave notes, including for the day of the crash, in Lubitz’s apartment. Germanwings said it had never received a sick note from Lubitz.

The big questions: What prompted Lubitz’s apparent decision to steer the plane down into the mountains? What health problems was Lubitz suffering from, and did they play any role in the crash?

The final moments

Over the weekend, the German newspaper Bild published a summarized transcript of what it claimed was the audio captured by the aircraft’s cockpit voice recorder.

It reports more details of what the pilots said than had previously been revealed, including Capt. Patrick Sondenheimer banging on the locked cockpit door and screaming, “For God’s sake, open the door!”

Officials haven’t officially released the audio from the cockpit voice recorder, and CNN cannot independently verify the information that Bild says is based on the 1.5 hours of sound captured by the device.

France’s accident investigation agency, BEA, told CNN it was “dismayed” by the voice recording leak to Bild. Martine Del Bono, a spokeswoman for the agency, said the BEA considered the report to be “voyeurism.”

According to Bild’s report, Sondenheimer told Lubitz that he didn’t manage to go to the bathroom before takeoff. Lubitz responded by saying that the captain could go anytime. After Sondenheimer leaves the cockpit, the plane starts to descend.

Lubitz didn’t say anything during the final descent, but the recording picks up his steady breathing, according to authorities.

The big question: What exactly happened inside the cockpit during those last minutes?

The investigation

Officials left Lubitz’s apartment Friday night with boxes of papers and evidence folders after spending about 90 minutes inside.

Investigators have said they still have interviews and other work to do before they can reveal what they gleaned from the records found in the apartment and at the home of Lubitz’s parents in the town of Montabaur, Germany. They are expected to question the co-pilot’s relatives, friends and co-workers.

Dusseldorf police said Saturday that a small team of French investigators had arrived in the city and that they were sharing information.

Jean Pierre Michel, lead investigator for the French inquiry, said in Dusseldorf that the French team would work in “full transparency” with their German counterparts.

Asked by a journalist about reports of Lubitz’s possible mental illness, he replied: “The elements of the investigation are strictly confidential and we cannot address these matters today.”

Michel said that no scenario could yet be ruled out, including mechanical failure, because investigators do not have “the necessary evidence.”

Searchers still haven’t found the plane’s flight data recorder, which stores a vast array of data about the aircraft’s performance and could provide investigators with vital information.

The big question: What will investigators eventually be able to prove about what happened on board Flight 9525?

The airline

Germanwings and its parent company, Lufthansa, are still reeling from the disaster. Senior managers are facing a barrage of questions about Lubitz and the company’s policies.

Lubitz passed his annual pilot recertification medical examination in summer 2014, a German aviation source told CNN.

An official with Lufthansa said that the exam only tests physical health, not psychological health.

The company was never given any indication Lubitz was depressed, the official said, and if he went to a doctor on his own, he would have been required to self-report if he had been deemed unfit to fly.

The company has already changed its rules following the crash to ensure that two crew members are in the cockpit at all times. Many other airlines have taken similar steps or been advised by authorities to do so.

The big questions: How much liability for the crash will Germanwings and Lufthansa face? Will other changes in airlines’ policies come about as a result of the Germanwings crash?

The people on board

More and more information is coming to light about the lives of the passengers and crew members on Flight 9525.

They include Iranian sports journalists who had been covering a big Spanish soccer game between Barcelona and Real Madrid; a group of students from a German town who were returning from a school trip; two successful German opera singers who had performed at a Barcelona theater; and an American mother and daughter from Virginia.

Most of the people on the flight were from Germany or Spain, officials have said.

Searchers at the mountainside crash site are continuing with their precarious mission to recover the remains of the dead.

Relatives of the victims and local residents have gathered for memorial ceremonies near the crash site in recent days.

The flight

Flight 9525, an Airbus A320, took off at 10:01 a.m. March 24 from Barcelona, bound for Dusseldorf. The plane had 144 passengers and six crew members on board.

According to French aviation accident investigators, the plane began descending from its cruising altitude of 38,000 feet at 10:31 a.m. It lost contact with French radar at an altitude of 6,175 feet at 10:40 a.m., the investigators said.

Transponder data shows that the autopilot was reprogrammed by someone inside the cockpit to change the plane’s altitude from 38,000 feet to 100 feet, according to Flightradar24, a website that tracks aviation data.

The aircraft crashed in a remote area near Digne-les-Bains in the Alpes de Haute-Provence region.