The Berlin Christmas market where a suspected Islamist extremist drove a truck into a crowd, killing 12 people, has reopened.
German police raided several locations overnight in the hunt for 24-year-old Tunisian suspect Anis Amri.
Amri is the subject of a Europe-wide arrest warrant. His ID and fingerprints were found in the lorry, officials say.
Police searched apartments believed to be linked to Amri in Berlin and the western city of Dortmund. About 80 officers searched a refugee centre in Emmerich, western Germany.
The German authorities have offered a reward of up to €100,000 for information leading to Amri's arrest, and warned he may be armed and dangerous.
Prosecutors denied reports by Bild newspaper that four people who were in contact with Amri had been arrested in Dortmund.
Amri's brother, Abdelkader Amri, speaking near the family home in Tunisia, urged his brother to give himself up, saying: "If he did what he is suspected of having done, he will be sanctioned and it will be a dishonour for us."
He was sure his brother was innocent, saying he left for Europe "for economic reasons... to work, to help the family. He didn't go for [terrorist] reasons".
Police installed concrete barriers at the Breitscheidplatz market to prevent a repeat of Monday's attack.
The lights were dimmed and the mood was sombre as the market reopened. Big crowds gathered there.
Candles and flowers were laid for those who died - they included at least six Germans, an Israeli tourist and an Italian woman - and the 49 people who were injured.
Surveillance reportedly called off
There is growing criticism of Germany's security services as details of emerge about Amri and his alleged links to Islamist extremists.
Amri, who arrived in Germany in 2015, was said to have been under surveillance by the Germany authorities from March to September this year on suspicion of planning a robbery to pay for automatic weapons for use in an attack.
The surveillance was reportedly called off after it turned up nothing more than drug-dealing in a Berlin park and a bar brawl.
Amri was said to have offered himself for a suicide attack, Spiegel reported, quoting communications intercepted for the prosecution of hate preachers in Germany.
What he said was not believed to be explicit enough for him to be arrested, the magazine said.
Amri was due to be deported from Germany in June, but stayed because there was a delay in receiving paperwork from Tunisia.
History of crime
Amri came to the attention of German counter-terror services after the arrest last month of extremist preacher Ahmad Abdelazziz A, known as Abu Walaa, who was charged with supporting so-called Islamic State (IS).
The Ruhrnachrichten news website said Amri lived in Dortmund from time to time. Residents at one block of flats said he 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.
He had a history of crime. He served four years in an Italian prison for arson and was 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.
IS said one of its militants carried out the attack, but offered no evidence.
Struggle in the lorry
It is thought Amri may have been injured in a struggle with the Polish driver of the lorry who was 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.