▲On the morning of March 24, 2015, Germanwings Flight 9525 left El Prat Airport in Barcelona. It was headed for Düsseldorf in Germany with 150 people on board.

▲The pilot then left the cockpit to go to the bathroom, leaving the plane in the hands of the co-pilot.

▲The 27-year-old co-pilot, Andreas Lubitz, should have had no problem keeping the flight on track during the pilot's short absence.

▲However, something happened in the cockpit while Lubitz was alone. According to flight records, Lubitz changed the plane's altitude as soon as the pilot left and slowly started to descend.

▲Within a couple of minutes, air traffic controllers noticed the loss of altitude and tried to make contact with the cockpit without success. They continued attempting to talk to Lubitz in the following minutes as they noticed he was also increasing the speed of the plane. He didn't respond.

▲At this point, the pilot returned from the bathroom and rang the bell to the cockpit, which is always locked for security reasons. Lubitz didn't answer him or open the door.

▲The recorder inside the cockpit captured the sound of the pilot trying to break down the door after a few minutes had passed with no response from Lubitz. Lubitz's steady breathing can be heard throughout.

▲The plane continued its descent, and the safety system warned that the plane was approaching the ground.

▲Soon after, the Germanwings plane crashed into the French Alps. Only 11 minutes had passed since Lubitz was left alone in the cockpit.

▲The plane crashed in a remote location on the Trois-Évêchés mountain range, located northwest of Nice.

▲Air traffic controllers quickly initiated a search mission when the plane disappeared from their radar. Within 20 minutes, a mountain rescue team was flying towards the crash site.

▲When they observed the smoking crash site, it was immediately clear that a plane had hit the mountain at full speed and there were no survivors.

▲News broke soon after that Andreas Lubitz may have purposefully crashed the plane, a revelation that shocked the world.

▲Within a few days of the crash, German police headed to Andreas Lubitz's house in the city of Montabaur and searched for any evidence or motive related to the crash.

▲It was discovered that Lubitz had a history of severe depression. A few years earlier he had taken a break from his pilot training to undergo treatment for his mental health. It was reported that he had suffered from a serious depressive episode and considered taking his own life. After working with a psychiatrist for several months and taking antidepressant medication, he was cleared to return to training.

▲Of the 150 people on the flight, 72 were German and 51 were Spanish. The rest of the victims were a mix of 16 other nationalities.

▲Among the victims was a group of high school students and teachers who were flying home to Germany after taking part in a Spanish language exchange program.

▲As investigators examined the wreckage, they concluded that it had been a strong collision. It's believed that the plane hit the mountain at 700 km/h (430 mph), resulting in instant death for everyone on board.

▲The theory that the co-pilot was responsible for the crash only gained traction as more details came to light.

▲One damning fact was that the plane's altitude was suddenly changed from 38,000 ft to 100 ft while Lubitz was alone in the cockpit. Experts confirmed that this change could only be done manually and deliberately.

▲The tragedy mobilized world press and leaders alike, who rushed to show their support towards the victims' families and friends.

▲After 9/11, cockpits were turned into impenetrable fortresses. After the Germanwings tragedy, there was a new consideration that those inside the cockpit might also pose a risk. New rules banning pilots from being alone in the cockpit were introduced by several airlines following the crash.

▲

Lufthansa, the parent company of the low-cost airline Germanwings, voluntarily paid out €75,000 (US$85,000) to each of the victim's families, as well as €10,000 (US$11,300) to all close relatives of the victims. Several families attempted to sue Lufthansa and the flight school attended by Lubitz, but it was ultimately found that their actions were not responsible for the crash.

▲

Investigators managed to find one of the plane's black boxes, which helped them piece together the details of what happened during that fateful 40-minute flight.

▲The Airbus 320 took off on its planned route over the sea towards France. The pilot monitored the plane's ascent for the first 30 minutes until they reached 38,000ft (11,600m).

▲

During the search of his home, investigators found a doctor's note in Lubitz's trash that declared him unfit for work and excused him on the day of the crash. It became clear that Lubitz was aware that he was experiencing issues, but decided to go to work anyway. The investigation concluded that he put prior thought into crashing the plane. Records from his flights prior to the crash showed that he had practiced reducing the altitude of the plane several times while alone in the cockpit.

▲

In addition, the descent was carefully controlled, which ruled out the possibility that the crash was caused by Lubitz's lack of ability.

▲

In 2017, a German artist installed a large sculpture at the crash site called Sonnenkugel, or "Sunsphere." It's made up of 149 gilded panels, one for each of the victims of the crash. A panel was not included for Lubitz, the 150th passenger on the plane.

Sources: (BBC) (GQ) (BBC)

▲

The passengers became agitated and scared as they noticed something was going wrong. Screams were picked up on the voice recorder.

▲

An infamous flight took off from Barcelona on March 24, 2015, and never arrived at its intended destination. Instead, the plane was involved in a devastating crash in the French Alps that killed everyone on board. Germanwings Flight 9525 was one of the worst tragedies in the history of air travel, but the horror only truly set in when the cause of the crash came to light. What first appeared to be a terrible accident was revealed to be a senseless crime of epic proportions.

Click through the following gallery to learn all about what happened on that fateful day.