As officials struggled Wednesday to explain why a jet with 150 people on board crashed amid a relatively clear sky, an investigator said evidence from a cockpit voice recorder indicated one pilot left the cockpit before the plane’s descent and was unable to get back in.

A senior French military official involved in the investigation described a “very smooth, very cool” conversation between the pilots during the early part of the flight from Barcelona, Spain, to Düsseldorf, Germany. Then the audio indicated that one of the pilots left the cockpit and could not re-enter.

“The guy outside is knocking lightly on the door, and there is no answer,” the investigator said. “And then he hits the door stronger, and no answer. There is never an answer.”

He said, “You can hear he is trying to smash the door down.”

“I don’t like it,” says a French official, who cautioned that his initial analysis was based on the very limited information currently available. “To me, it seems very weird: this very long descent at normal speed without any communications, though the weather was absolutely clear.”

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