• 9:45 a.m.: A Dusseldorf medical facility says that contrary to reports, it didn't treat Andreas Lubitz for depression.
• 8:49 a.m.: Germanwings says it didn't receive a sick note for the day of the flight.
• 7:57 a.m.: A letter found in a waste bin in Lubitz's apartment indicated he "was declared by a medical doctor unfit to work," Dusseldorf prosecutor Christoph Kumpa said.
• 6:23 a.m.: Lufthansa, together with other German airlines, has announced the immediate introduction of new rules for the cockpit. It will now be a requirement for there to be two authorized people in the cockpit at all times.
• 5:01 a.m.: The medical leave notes issued by a doctor for Lubitz included the day of the crash, the Dusseldorf public prosecutor's office said.
• 5:01 a.m.: The prosecutor's office did not say if the medical leave note related to a physical or a mental health issue but said Lubitz appeared to have been under treatment by a doctor for some time.
• 5:01 a.m.: The fact that Lubitz appears to have ripped up recent medical leave notes "leads to the preliminary conclusion that the deceased kept his illness secret from his employer and his professional environment."
The Germanwings co-pilot accused of intentionally setting a plane on a fatal descent in the French Alps had an illness that he kept secret from his employer, German prosecutors said Friday.
A statement from the Dusseldorf public prosecutor's office did not say what the illness was, nor whether it was a physical or mental health issue.
But documents found in a search of Andreas Lubitz's home and that of his parents "indicate an existing illness as well as adequate medical treatment thereof," the prosecutor's office said.
The fact that investigators found "ripped, recent medical leave notes, including for the day of the offense (crash), leads to the preliminary conclusion that the deceased kept his illness secret from his employer and his professional environment."
Dusseldorf prosecutor Christoph Kumpa said a letter found in a waste bin in Lubitz's Dusseldorf apartment "indicated that he (Lubitz) was declared by a medical doctor unfit to work."
The letter was found "slashed" in the dustbin, Kumpa told reporters in English.
Lubitz's employer, Germanwings, issued a statement Friday saying the company didn't get a sick note from Lubitz for the day of the Barcelona-to-Dusseldorf flight, which crashed Tuesday, killing 150 people.
Asked earlier Friday about news reports citing unnamed sources that queried Lubitz's mental health, a Germanwings representative told CNN the company could not go into specifics about his medical record for reasons of confidentiality.
"The pilots had a clean bill of health, and all medical data is subject to medical confidentiality," a representative said. "We can't confirm or deny this report due to medical confidentiality."
Also, a Dusseldorf medical clinic said it had not treated Lubitz for depression, despite media reports indicating it had. The University Clinic said that Lubitz was most recently at the clinic on March 10 and that the visit concerned an unspecified diagnosis.
During their search of the Lubitz family home in Montabaur and Lubitz's Dusseldorf apartment, authorities took away several objects and papers, German police said.
Objects taken will be examined, "which might lead to more information," Marcel Siebig, of Dusseldorf police, said Friday.
Marseille prosecutor Brice Robin, who is overseeing the criminal investigation into the crash in France, said the documents would be handed to French authorities. Two French police officers are on their way to collect the evidence, he said.
Police stood guard Friday outside the apartment, in a quiet suburban neighborhood with a handful of small businesses, restaurants, running trails and a lake nearby.
Residents told CNN there is not much to do in the area and most people around Lubitz's age would go to the city center, about 20 minutes away, for nightlife or dining. No neighbors said they either knew Lubitz or had seen him around.
His parents' home in Montabaur, where Lubitz grew up, was also under police guard Friday. A bouquet of flowers and a candle had been left by the doorstep, but the windows were shuttered.
A day after Robin revealed that cockpit audio showed that Lubitz apparently "wanted to destroy the aircraft," many chilling questions remain unanswered.
Did he plan his actions? What drove the 27-year-old German national to do that?
'Clean bill of health'
Lufthansa, together with other German airlines, announced Friday the immediate introduction of new rules for the cockpit. It will now be a requirement for there to be two authorized people in the cockpit at all times.
A CNN employee said the captain on a Friday morning Germanwings flight from Zurich, Switzerland, to Cologne, Germany, announced that he would like to "reassure passengers that there will be two people present in the cockpit at all times."
An official with the German Aviation Association told CNN that it was only a matter of hours, or a day at most, for this rule to be implemented across all big German airlines.
Emotions were still raw outside the Germanwings headquarters in Cologne on Friday.
The German Airline Pilots Association, Vereinigung Cockpit, earlier warned in a statement against leaping to conclusions based only on a "first glimpse," from the cockpit audio, into what happened on the flight deck.
"We should not rush to conclusions based upon limited data. The reasons that led to this tragic accident will only be determined after all data sources have been thoroughly examined" said Ilja Schulz, the group's president.
The group called for the plane's second "black box," the flight data recorder, to be found and examined as soon as possible. Only once the investigation is complete should work start on new procedures to prevent another such tragedy, it said.
Amid all the questions, some answers emerged Thursday.
It's unknown whether Lubitz planned his actions, Robin said. But he "took advantage" of a moment in which the pilot left the cockpit and "activated the descent," which can only be done intentionally.
Transponder data showed the autopilot was reprogrammed by someone in the cockpit to change the plane's altitude from 38,000 feet to 100 feet, according to Flightradar24, a website that tracks aviation data.
"We at Lufthansa are speechless that this aircraft has been deliberately crashed by the co-pilot," said Carsten Spohr, CEO of Lufthansa, which owns Germanwings.
Banging and screaming
The plane's cockpit audio recorder captured horrific sounds. The captain, who was locked out of the cockpit, banged on the door to be allowed in, the Marseille prosecutor said.
Lubitz's breathing was steady, with no sign that he had a heart attack or other medical issue.
Scared passengers can be heard screaming on the audio recording for the final few moments of the flight.
The most plausible explanation is that Lubitz, "through deliberate abstention, refused to open the cabin door ... to the chief pilot, and used the button" to cause the plane to lose altitude, Robin said.
The disaster is not being described as a "terrorist attack," and the killing of 150 people would generally not be described as a "suicide" either, Robin said.
If a person kills himself and 149 others, the word "suicide" should be replaced with another word, Spohr said.
Officials said Lubitz was not known to be on any terrorism list, and his religion was not immediately known.
Missing flight data recorder
Once found, the flight data recorder could shed more light on the plane's final minutes.
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.
The 144 passengers and six crew members came from 18 countries. About half were from Germany, and 49 were from Spain, according to Spain's Security Secretary Francisco Martinez. Three were Americans.
The French government has asked the FBI to help investigate the crash, a law enforcement official said.
No psychological testing after hiring
Lubitz had trained at the Lufthansa flight center in Bremen, Germany. He had been with Germanwings since September 2013 and had completed 630 hours of flight time, the company said.
He only had about 100 hours of experience on the type of aircraft he was flying, but he had all the necessary certifications and qualifications to pilot the aircraft alone, the prosecutor said.
He had passed medical tests, Spohr said.
Lufthansa does not have standard psychological testing for pilots once they are hired, Spohr said. The company considers an applicant's psychological state when hiring, he said.
The co-pilot was "fully qualified to pilot the aircraft on his own," Robin said.
Village opens homes
Relatives and friends of the victims traveled on special Lufthansa flights to an area near the site where their loved ones perished.
They held prayers in Le Vernet, near Seyne-les-Alpes, a village serving as a staging post for the recovery operation. Flowers and pictures sat on the ground, candles flickering in the cold air Thursday night.
Germanwings said Thursday it was setting up a family assistance center in Marseille, with family briefings to start Saturday. Another flight carrying victims' relatives was due to arrive in Marseille from Barcelona on Friday.
"Our focus in these darkest hours is to provide psychological assistance to the families and friends of the victims," said Thomas Winkelmann, a spokesman for the Germanwings executive board.
The bodies will not be released to family members until all DNA identification work has been done -- a process likely to last several weeks, Robin said.
While some human remains have been recovered, many have not. The task is treacherous for search crews working on steep slopes in icy weather. Workers were dropped by helicopters and tied together for safety.