The plane from the Slovenian capital Ljubljana landed at an airport in Germany.
A suspicious conversation overheard by airline staff sparked the alert.
All 151 passengers were rushed off the plane on emergency slides.
Once evacuated, there were taken to a transit gate and checked by police.
Take-offs and landings were suspended for three hours at Cologne-Bonn airport.
Police also destroyed a piece of baggage that couldn’t be assigned to anybody on board.
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