German police are hunting a Tunisian man over the Berlin market attack after finding documents in the truck, according to reports.
The identity document was found under the driver's seat of the truck which ploughed into crowds at the Christmas market on Monday evening, killing 12 people.
Der Spiegel and Allgemeine Zeitung reported that the document, apparently asylum office papers announcing a stay of deportation, was in the name of Anis A, born in 1992 in Tataouine, Tunisia.
The suspect was also known to have two aliases, according to the newspapers.
Bild said Anis A was known to police for bodily harm and is considered dangerous.
"No one will rest until the perpetrator or perpetrators have been caught," German Interior Minister Thomas De Maiziere told ARD public television.
It comes after the sole suspect - a 23-year-old Pakistani asylum seeker - was released due to lack of evidence.
He had been picked up near the popular market, next to the Kaiser Wilhelm Memorial Church, after police had been given a description by witnesses.
Following the suspect's release, Berlin police chief Klaus Kandt told ARD "one or more" perpetrators were believed to be on the run and possibly armed.
Witnesses saw only one man flee from the truck after it hurtled through the market for 60 to 80 metres (200 to 260ft) before coming to a stop in Breitscheidplatz.
A Polish man who had been driving the lorry before it was apparently hijacked was found dead in the cab. He had been apparently stabbed and shot with a pistol, which is also still missing.
In addition to the Polish truck driver, who has been named as Lukasz Urban (37) six of the people killed were German.
Of the other five who died, one of the victims is feared to be an Italian woman.
Twenty-four injured remain in hospital, 14 of whom are in critical condition. Israel and Spain have also said their nationals were among those injured.
Islamic State claim
Islamic State claimed responsibility for the attack. Its news agency Amaq said one of its "soldiers" carried out Monday evening's deadly crash "in response to calls for targeting citizens of the crusader coalition".
US State Department spokesman John Kirby said that while the attack "bears the hallmarks of previous terror attacks," US officials did not have enough information to back up the claim of responsibility.
Several German policemen were seen late on Tuesday searching a location in Berlin where the lorry had apparently been parked before the attack.
Officers used flood lights to comb the bank of a canal next to Friedrichkraussufer street.
The spot, in an industrial area of central Berlin, was apparently provided to the police by the company that owned the Scania truck.
Die Welt said Mr Urban had loaded steel beams on to his trailer in Turin, before setting off for the Berlin branch of ThyssenKrupp Schulte.
The boss of the firm that owns the lorry said the driver - his cousin - reported arriving a day too early and being sent away.
Investigators have been able to examine the route of the lorry just before the attack and found the driver did not take the shortest route to Breitscheidplatz.
He travelled through Berlin for about half an hour - twice as long as necessary.
Investigators believe that the perpetrator was an untrained truck driver and took the time to test the vehicle before the attack, Die Welt said.
The autopsy of the Polish truck driver showed that he had tried to fend off the perpetrator shortly before the crash that left so many dead and injured, Bild reported.
An investigator told the newspaper the terrorist drew a knife and stabbed the driver several times, possibly because the Pole grabbed the steering wheel in an attempt to protect human life.
The Christmas market is understood not to be monitored by video, so there is no national or local government CCTV footage of the crime or the escape of the alleged perpetrator.
Investigators have appealed for anyone who took photographs or video on the night to get in touch.
A further post mortem is due to take place that should clarify the exact time of death of the Polish driver and investigators are yet to carry out a full evaluation of the GPS data to clarify the route the lorry took.
Chancellor Angela Merkel, who laid white roses at the scene on Tuesday afternoon, said she was "shocked, shaken and deeply saddened" by the attack - one of a number in Germany this year.
It comes five months after 86 people died in Nice when a truck mowed people down on the French city's seafront. Islamic State claimed responsibility.
