This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

PARIS, France — Investigators  say the pilot believed to intentionally crashed an Airbus A320 hid an illness from the airline.

here are indications that the co-pilot of the Germanwings aircraft that crashed into the French Alps Tuesday hid an illness from his employers, German prosecutors said in a statement Friday morning.

There are reports a torn up note excusing Andreas Lubitz from work the day of the crash was found in his apartment in Germany.

“We have found something which will now be taken for tests. We cannot say what it is at the moment but it may be very significant clue to what has happened,” Markus Niesczery, a spokesman for Dusseldorf Police, told the Daily Mail late Thursday.

German tabloid Bild quoted Lufthansa sources to say Lubitz spent a year and a half in psychiatric treatment.

No suicide note was found.

Lufthansa Chief Executive Carsten Spohr confirmed Lubitz took 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.

Lubitz is a German national and had 100 hours of experience on the plane.

One pilot was locked out of the cockpit.

Pounding could be heard on the cockpit door before the crash.

Passengers could be heard screaming on a  flight recording .

Here’s a timeline of what happened:

• 8:34 p.m. ET: Lufthansa, the parent company of Germanwings, does not have any information about The New York Times article reporting that one of the pilots on Germanwings Flight 9525 was locked out of the cockpit when the plane crashed, company spokesman Klaus Gorny told CNN Thursday. Lufthansa is looking into the report, Gorny said.

• 7:51 p.m. ET: One of the pilots on board Germanwings Flight 9525 was locked out of the cockpit when the plane crashed Tuesday, a senior military official told The New York Times, citing evidence from the cockpit voice recorder.

• 7:01 p.m. ET: Helicopters have airlifted some victims’ remains from the site of the Germanwings plane crash in the French Alps, the Gendarmerie said Wednesday, according to CNN affiliate France 2.

Full story:

Investigators trying to determine what caused the crash of Germanwings Flight 9525 have made a startling discovery in an audio recording, according to a New York Times report: One of the plane’s pilots was locked out of the cockpit before the crash.

“You can hear he is trying to smash the door down,” a senior military official involved in the investigation told the newspaper, describing audio from the cockpit voice recorder, one of the plane’s black boxes.

“We don’t know yet the reason why one of the guys went out,” the official said, according to the Times’ report. “But what is sure is that at the very end of the flight, the other pilot is alone and does not open the door.”

Lufthansa spokesman Klaus Gorny said the company has no information about the report but is looking into it.

The Times’ report is a “terribly shocking revelation,” CNN aviation analyst Peter Goelz said. But he and other experts cautioned that it’s still unclear what could have been going on inside the cockpit.

Possibilities range from a medical emergency to something more nefarious, CNN aviation correspondent Richard Quest said.

French authorities revealed Wednesday that they’d been able to access audio from the recorder, even though its external casing was damaged.

Finding the plane’s second black box will also be critical to understanding the mystery of what went on inside the jet.

That box, the flight data recorder, hasn’t been found yet, but Lufthansa CEO Carsten Spohr said Wednesday that there’s a high probability it will be.

Investigators scoured dangerous terrain in the French Alps as they searched for clues in the wreckage.

Workers dropped to the crash site from helicopters and had to be tied together because the steep area in the mountains is so treacherous, said Remi Jouty, head of the BEA, the French aviation investigative arm leading the probe.

Spohr said Tuesday’s plane crash “represents the darkest hours” in the history of his company, which owns Germanwings.

Officials are struggling to understand how an airplane that “was in perfect technical condition” with two experienced pilots “was involved in such a terrible accident,” he said.

But even worse, he said, is seeing the heartbreak of the relatives and friends of the victims who perished in the crash.

“What they have gone through is, of course, incomprehensible,” he said, describing what he said was an emotional meeting between the relatives and airline executives Wednesday.

And now, he said, the company’s focus will be taking care of them.

Special Lufthansa flights will take relatives and friends of victims to southern France on Thursday, so they can be near the search scene, he said.

“We need to understand what happened,” French President Francois Hollande said. “We owe that to the families.”

The doomed flight was traveling from Barcelona, Spain, to Dusseldorf, Germany, when it crashed Tuesday in the French Alps.

Germanwings said the plane reached its cruising altitude of 38,000 feet, and then dropped for about eight minutes. The plane lost contact with French radar at a height of about 6,000 feet. Then it crashed.

There were 150 people from 18 countries on board.

Teams have begun the daunting task of identifying the victims’ bodies, but caution that it could take time to complete.

Investigators are still trying to piece together what caused the crash.

Jouty, the head of the investigation team, said the debris suggests the plane hit the ground and then broke apart, instead of exploding in flight.

Radar followed the plane “virtually to the point of impact” in the Alps in southern France, Jouty said. The flight’s last altitude recorded by radar was just over 6,000 feet.

Officials have said that while they have not ruled out terrorism, it seems unlikely.

FBI agents based in France, Germany and Spain are looking through intelligence sources and cross referencing the passenger manifest of Germanwings Flight 9525, two senior law enforcement officials said. So far, their search hasn’t turned up anything that “stands out” or anything linking the passengers to criminal activity, according to one official.