Investigators found fingerprints of a Tunisian suspect in the Berlin Christmas market attack on the door of the truck that ploughed through the crowds, killing 12, German media reports say.
Islamic State has claimed responsibility for the attack in which a truck smashed through wooden huts selling gifts, mulled wine and sausages on Monday evening. It was the deadliest attack on German soil since 1980.
A nationwide manhunt for the migrant is underway.
The media did not name their source for the report about Amri’s fingerprints, and police declined to comment when contacted by Reuters.
The Berlin market reopened on Thursday ringed by concrete bollards.
Arrests made in Dortmund
Police in the northwestern German city of Dortmund arrested four people who had been in contact with Amri, media reports said, but a spokesman for the chief federal prosecutor denied that and said he would give no further details on the operation to avoid jeopardising it.
Bild newspaper cited an anti-terrorism investigator as saying that it was clear in spring that the Tunisian suspect — 24-year-old Anis Amri — was looking for accomplices for an attack and was interested in weapons.
The report said preliminary proceedings had been opened against Amri in March based on information he was planning a robbery to get money to buy automatic weapons and “possibly carry out an attack with them and other accomplices”.
In mid-2016, he spoke to two IS fighters, and Tunisian authorities listened in on their conversation before informing German authorities. Amri also offered himself as a suicide attacker on known Islamist chat sites, Bild said.
Police started looking for the Tunisian after finding an identity document under the driver’s seat of the truck used in the attack. Authorities have stressed that Amri is just a suspect and not necessarily the driver of the truck.