German police are apparently searching for a Tunisian man in his 20s in connection with the Berlin Christmas market atrocity.
Reports suggest a temporary-stay permit potentially identifying him was found in the cab of the truck that was used to slaughter a dozen people and injure 49 others at the Breitscheidplatz market on Monday night.
The man has been named only as Anis A. He was apparently born in 1992 in the city of Tataouine, southern Tunisia.
A police operation is believed to be under way in the state of North Rhine-Westphalia where the permit was issued.
Reports say the suspect may have been injured in a struggle with the driver whose truck he hijacked.
According to German newspapers Allgemeine Zeitung and Bild, the Tunisian suspect is aged 21 or 23 and is known by three different names.
Islamic State (IS) has claimed responsibility for the attack but has offered no evidence.
German Interior Minister Thomas de Maiziere said he was confident that the person responsible would be caught soon.
If the terrorist turns out to be Tunisian, it will be the second such attack this year committed by a man from the north African country.
In July 86 people were killed and 434 were injured in Nice when Tunisian terrorist Mohamed Lahouaiej-Bouhlel drove a truck into a crowd.