Dusseldorf prosecutor Christoph Kumpa said that on one day Lubitz also "searched for several minutes with search terms relating to cockpit doors and their security measures."
Police analysis of the correspondence and search history on the device, retrieved from Lubitz's Dusseldorf apartment, demonstrated that the co-pilot used it from March 16 to March 23, Kumpa said.
The search history was not deleted and also revealed searches concerning medical treatment, the prosecutor said.
Lubitz is suspected of deliberately bringing down Germanwings Flight 9525 in the French Alps on March 24, killing all 150 on board. Investigators have since focused on his health as they try to establish his motivation.
Noting he's made a criminal request to German authorities but is for now conducting his own investigation, the prosecutor in Marseille, France, said he is tasked with an involuntary homicide investigation. But prosecutor Brice Robin noted that Lubitz made voluntary actions -- such as guiding the plane toward the mountain and reducing its speed to prevent alarms from going off -- and was "alive and conscious" to the very end.
A European official government official with detailed knowledge of the investigation said that Lubitz's actions amount to"premeditated murder."
While cautioning that there are still many holes in understanding Lubitz's motivation, the disclosures about his Internet searches show that he planned to do what he was going to do, according to this official.
Second 'black box' found
As authorities try to figure out what was on Lubitz's electronic devices, they got another big break about what was happening inside Airbus 320 that went down -- its flight data recorder.
The jetliner's cockpit voice recorder was located shortly after the plane crashed. Now, investigators have both "black boxes," as the devices are called, and the details that they might provide.
A female police officer digging by hand for clothes in a ravine that been searched previously found the flight data recorder on Thursday afternoon about 8 inches (20 centimeters) below the surface, Robin told reporters.
Normally white with florescent orange, this discovered recorder lived up to its name as a black box because fire had darkened it with ashes. Even with this damage, the Marseille prosecutor said that investigators should be able to get useful information out of it.
"We will be able to identify the speed, the altitude and the way the pilot acted ... which will be critical," said Robin.
Prosecutor: 150 sets of DNA recovered
The voice data recorder is one of many items uncovered at the crash site in the southern French Alps.
Authorities have found 470 personnel effects there, according to Robin. That number includes 40 cell phones, though all those were badly damaged. Robin cast doubt that any useful information could be retrieved from those phones, given their condition.
This is consistent with French officials' claims Wednesday insisting that two publications, German daily Bild and French Paris Match, were wrong to report that cell phone video
showed the harrowing final seconds from on board the flight.
More importantly, investigators have isolated 150 different sets of DNA -- a number that corresponds with the number of people on Flight 9525. Still, the Marseille prosecutor cautioned, "It doesn't mean we have identified 150 victims. We need to compare (the recovered DNA to) DNA from the families and the deceased."
Robin estimated "it will take between three to five weeks, if all goes well" for the passengers' loved ones to get the remains.
But the mourning is already underway.
A memorial stone set up in the village of Le Vernet, the nearest accessible point to the crash site, has become a place of pilgrimage for those with relatives and friends on board the plane.
People in the German town of Haltern recently came together for a memorial service to remember 16 students and two teachers lost in the crash.
Push to take steps to prevent a repeat
Providing some closures to the families of those passengers and crew members is a top priority for authorities.
So, too, is doing what they can to figure out why this happened and prevent similar tragedies.
There are new calls from aviation experts to develop and deploy enhanced crash avoidance software that could take control of an aircraft away from a pilot and steer it to a safe altitude.
The technology would work in a similar fashion to crash avoidance technology
already used in automobiles if a pilot is incapacitated or ignores audible warnings.
The idea is not new. In fact more than 10 years ago following 9/11, Airbus, the manufacturer of the doomed aircraft, was working to develop aircraft crash avoidance software with tech giant Honeywell -- in part to prevent jetliners from being flown into large buildings or mountains. But the project was ultimately scrapped.
Still, there's also a widespread view that the best way to understand what happened in this case is to understand Lubitz.
Source: Lubitz saw multiple doctors
It is becoming increasingly clear to investigators that Lubitz was "very afraid" he would lose his license to fly because of his medical issues, a law enforcement source with detailed knowledge of the investigation told CNN.
It's already emerged that Lubitz had battled depression
years before he took the controls of Flight 9525 and that he had concealed from his employer recent medical leave notes saying he was unfit for work.
But the law enforcement source said that after a severe depressive episode in 2009, Lubitz relapsed with severe depression and stress in late 2014.
In the weeks leading up to the crash, Lubitz was shopping doctors, seeing at least five, perhaps as many as six, the source said, as he kept going from one doctor to the next seeking help.
The 27-year-old was having trouble sleeping, and one of the doctors he saw recently was a sleep specialist, the law enforcement source said. Lubitz apparently told some doctors that he was afraid of losing his pilot's license because of his medical issues.
The doctors knew he was a pilot and gave him a "not fit to work" notice, which he was apparently required to give to his employer, even though he didn't, the source said. Officials have found doctors handled the matter the way they were supposed to and found no negligence on their part.
Thinking he would stay home from work based on the sick notes, Lubitz was prescribed a lot of medication, including "heavy depression medicine" that would have been "very heavy" on the body and "critical to a pilot," the source said.
However, the law enforcement source doesn't think Lubitz was using the medicine while working, because investigators interviewed a pilot he flew with the day before who said he was "completely normal" with no problem whatsoever.
Inside Lubitz's apartment, investigators found a couple of notes with only a few words, involving stress and his pilot's license, the source added. He didn't know if Lubitz wrote these down while talking to someone on the phone or wrote the memo to remind himself of something.
Lubitz told his Lufthansa flight training school in 2009 that he had a "previous episode of severe depression," the German airline confirmed Tuesday. Lufthansa is the parent company of budget airline Germanwings.
German officials announced that a new task force would look at issues including medical procedures for pilots and cockpit door locking mechanisms after the devastating crash.
The cockpit voice recorder revealed that Lubitz had locked the pilot, Patrick Sondenheimer
, out of the cockpit before putting the plane into its fatal descent, said Robin, the Marseille prosecutor.
Cockpit doors on planes were strengthened following the events of September 11, 2001, making it impossible for the captain to force his way in.
German Transport Minister Alexander Dobrindt told the news conference Thursday that the task force would prioritize questions around the cockpit door locking mechanism and procedures for checking pilots' medical and psychological well-being.
It would seek to move quickly, he said, but would not make rash decisions.
Klaus-Peter Siegloch, head of the German Aviation Association, emphasized issues around confidentiality when it comes to a pilot's medical records.
"The confidence our pilots have in our medical doctors is of high importance," he said. "I believe if there is a lifting of doctor-patient confidentiality, then possibly pilots will not trust in medical doctors and that will make the situation worse."
The task force will bring together government officials with representatives of the German airline companies, the German Aviation Association and the Federation of German Airlines.