German police are looking for a Tunisian man after finding an identity document under the driver's seat of the truck which ploughed into a Christmas market on Monday evening, killing 12 people, Der Spiegel's online edition reported on Wednesday.
Der Spiegel, which did not cite its sources, named the person identified in the document as a young man born in Tataouine.The man is also believed to use false names.
Berlin police said they had received more than 500 leads about the crime.
Andre Schulz, the head of the German Union of Detective Constables, said investigators were analysing DNA traces and fingerprints, as well using GPS data from the evening of the attack to trace the perpetrator's mobile phone.
"We have many ways to find this person," Schulz said.
Security sources have told news agency DPA that police are planning an "imminent" operation in the German state of North Rhine-Westphalia related to the attack.
German police also arrested a second suspect over the attack on a Christmas market in Berlin that killed 12 people but later released him, German broadcaster rbb reports.
On Tuesday evening police also released a Pakistani asylum-seeker who was arrested near the scene shortly after Monday's attack and authorities warned the attacker is on the run and may be armed.
