Lorry was “intentionally” driven into a Christmas market in Berlin, killing at least 12 people and injuring 48, police believe.
A man found dead in the lorry’s cab was a Polish citizen.
Police said the man, who has not been named, was not driving when the crash happened.
A second man was arrested shortly afterwards say reports.
Islamic State claimed responsibility for the attack.
Five months ago 86 people died in Nice, France, when a truck mowed people down on the city’s seafront.