The co-pilot of the Germanwings flight that crashed this week in the French Alps deliberately put the plane into its fatal descent, a French prosecutor said on Thursday.

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The Associated Press reported that Marseille prosecutor Brice Robin said the co-pilot had “intentionally” set the plane into the descent on Tuesday that ended with it crashing into a mountainside near Nice, France.

The co-pilot seemed to want to “destroy the plane,” he said.

"There's nothing to suggest a terrorist attack ... but we'll see," he added.

Officials said that the co-pilot, who authorities identified as 28-year-old Andreas Lubitz, was a German who had not been labeled as a terrorist.

The flight from Barcelona, Spain, to Dusseldorf, Germany, was carrying 150 people — 144 passengers and 6 crew members — when it crashed into the mountain at a high speed.

The co-pilot had purposefully not opened the cockpit door for the flight’s captain as the plane descended, authorities said. Robin said that the co-pilot was totally silent during the descent, and appeared to be breathing normally.

“I think he refused to open the door and turned the button to get down the plane. It was a voluntary action on the part of the co-pilot,” Robin said, according to The Guardian.

On Wednesday, a military official told The New York Times that the captain could be heard pounding on the door in the final moments of the flight.

--This report was updated at 8:30 a.m.