Details are slowly emerging Thursday about a 28-year-old German national who officials believe purposely crashed Germanwings Flight 9525.

Andreas Lubitz was alone at the controls of the Airbus A320, officials said — and died along with all 144 passengers and five fellow crew members — when it plunged into the French Alps Tuesday.

It seems that Lubitz “wanted to destroy the aircraft,” Marseille prosecutor Brice Robin said, but it’s unclear why.

Information gleaned from the aircraft’s mangled cockpit voice recorder revealed that the captain, who has not been identified, left the cockpit, probably to use the restroom, the prosecutor said.

When the captain returned, he couldn’t get back inside. He banged on the door but Lubitz did not open the door, Robin said.

The co-pilot “manipulated the buttons of the flight monitoring system to activate the descent of the aircraft,” Robin said. “The action can only be voluntary.”

That Lubitz could have voluntarily crashed a plane was dumbfounding to fellow pilots who knew him.

There’s no reason to believe, at this time, that Lubitz’s motives were terrorism-related, the prosecutor said. His name wasn’t on any terror list.