Marseille's prosecutor Brice Robin entered the room with no sign that he had an astonishing conclusion to reveal. He told reporters he had examined the voice recordings of the last 30 minutes of the flight. For the first 20 minutes, Mr Robin said, the captain and co-pilot spoke to each other normally - even cheerfully. Then the captain got up - apparently to use the toilet - and the cockpit door locked behind him. The co-pilot Andreas Lubitz was left alone in control of the plane. He soon pressed a button for the aircraft to descend. The prosecutor said he believed that this was a deliberate act.

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The recordings picked up every detail of the co-pilot's actions - suggesting that he was conscious and alert. "We could hear him breathing. He breathed normally. He didn't utter a single word the minute the pilot left the cabin," Mr Robin said. The plane started to descend. The captain knocked on the cockpit door and used the intercom. But his co-pilot didn't respond. Trapped outside his own cockpit, the captain became increasingly desperate. "The alarms went off to alert the crew to the proximity of the ground and at that moment, we could hear a violent knocking on a door, someone was trying to force the door. It was a strong door, it was reinforced, in line with international norms, to protect against acts of terrorism." That meant there was no way in - and no way to stop the co-pilot. Andreas Lubitz calmly flew himself, his captain and their 148 crew and passengers straight into the mountainside.

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"I think that the victims did not realise what was happening until the last moment, the very last moment. Because in the recording, we could only hear the cries at the last moment, just before the impact with the ground." The prosecutor described their deaths as sudden and immediate. Brice Robin said he believed that Andreas Lubitz deliberately crashed the plane. If that turns out to be true, the final 10 minutes of the 28-year-old co-pilot's life were a sustained act of mass murder.