The Berlin Christmas market where 12 people were killed on Monday by a suspected Islamist extremist who drove a truck into a crowd has reopened.
Police have installed concrete barriers to prevent a repeat attack.
Meanwhile police have raided homes in the city of Dortmund, but prosecutors denied reports that arrests linked to a Tunisian suspect were made.
Anis Amri's ID was left in the lorry and now his fingerprints have been found on the door, reports say.
The attack at the Breitscheidplatz market killed 12 and injured 49 more. The victims included at least six Germans and an Israeli tourist.
On Thursday morning, police raided properties in the western city of Dortmund.
Bild newspaper quoted the federal prosecutor's office as saying four people who were in contact with Amri had been arrested.
However, a spokesman for the prosecutor's office denied the report, saying he was not aware of any arrests.
There were also raids at a migrant centre in Emmerich in western Germany, where Amri stayed briefly last year, and at addresses in Berlin.
Amri's name came to the attention of German counter-terror services last month and he reportedly moved in the circle of extremist preacher Ahmad Abdelazziz A, known as Abu Walaa, who was arrested last month and charged with supporting so-called Islamic State (IS).
The Ruhrnachrichten news website said he had lived in Dortmund from time to time and residents at one block of flats said he had spent time with a German of Serbian origin, Boban S, who was arrested last month along with Abu Walaa.
Amri was on a US no-fly list, had researched explosives online and had communicated with IS at least once via the Telegram Messenger service, the New York Times reported.
IS has said one of its militants carried out the attack but has offered no evidence.
Amri had also offered himself for a suicide attack, Spiegel magazine reported, quoting communications intercepted for the prosecution of hate preachers in Germany.
However, what he said was not believed to be explicit enough for him to be arrested, the magazine said.
Amri had also been put under surveillance in Germany earlier in the year on suspicion of planning a robbery to pay for automatic weapons for use in an attack.
But the surveillance was reportedly called off after it turned up nothing more than drug-dealing in a Berlin park and a bar brawl.
Amri is said to have entered Germany last year and was due to be deported in June but stayed because there was a delay in receiving paperwork from Tunisia.
He had a history of crime, serving four years in an Italian prison for arson and convicted in absentia in Tunisia for a violent robbery.
A police notice lists six different aliases used by Amri, born on 22 December 1992, who at times tried to pass himself off as an Egyptian or Lebanese.
The German authorities warn he could be armed and dangerous and are offering a reward of up to €100,000 (£84,000; $104,000) for information leading to his arrest.
It is thought Amri may have been injured in a struggle with the Polish driver of the lorry, found murdered in the cab.
Investigators believe the lorry was hijacked on Monday afternoon when it was parked in an industrial zone in north-western Berlin pending delivery of its cargo.