A Europe-wide manhunt is under way for the Tunisian man wanted for the Berlin lorry attack, who had been under surveillance earlier this year, media reports say.
Anis Amri, 24, was reportedly monitored on suspicion of planning a robbery in order to pay for guns but surveillance was lifted for lack of evidence.
Before entering Germany, he had served four years for arson in Italy.
Monday evening’s attack at a Christmas market killed 12 and injured 49 more.
An arrest warrant was issued after Anis Amri’s residence permit was found in the cab of the lorry that left a trail of carnage at a Christmas market near Berlin’s most famous shopping street, the Kurfuerstendamm.
Reports suggest he may have been injured in a struggle with the Polish driver of the lorry, found murdered in the cab.
Chancellor Angela Merkel has met her security cabinet to discuss the investigation into the attack.
In another development, the German cabinet approved plans agreed last month to allow more video surveillance of public places.
Where Amri stayed: Gavin Lee, BBC News, Emmerich
In a small detached building surrounded by fields, 16 male migrants live on two floors in basic, student-style accommodation. I knocked on each of their doors, The young Iraqi and Albanian refugees who answered claimed they knew little about Anis Amri, who stayed here for a short time.
„I don’t recognise his face,“ Andi from Albania told me as I showed him a picture of the Berlin suspect. „But we’ve been talking about this attack with other refugees,“ he added, „and about how this man had jihadist contacts around here. Maybe he did. It’s horrible around here. We hate it but no one here knew much about him.“
There is a swastika graffiti sign on the corridor wall, evidence of anti-migrant sentiment, which migrants say was done by locals two months ago.
The site’s night manager, who did not want to be identified, told me he had recognised Amri „straightaway“ because „We’re a small place. I know everyone who stays here.“ Staff said Amri had „disappeared“ after „a brief stay“.
We are told that police officers attempted to search the premises earlier today but left because of mistakes on their paperwork. They have not returned. This place offers a glimpse into the life and activity of Europe’s most wanted terror suspect but it appears to be a trail that goes cold quickly.
German judicial sources say the suspect, who reportedly entered Germany last year, was monitored in Berlin between March and September on suspicion of planning a robbery to pay for automatic weapons for use in an attack.
Surveillance was reportedly called off after it turned up nothing more than drug-dealing in a Berlin park and a bar brawl before the suspect disappeared from his regular haunts in Berlin.
Ralf Jaeger, the interior minister of North Rhine-Westphalia, confirmed that Anis Amri had, more recently, attracted the attention of counter-terrorism police.
„Security agencies exchanged their findings and information about this person with the Joint Counter-Terrorism Centre in November 2016,“ the minister said.
Sueddeutsche Zeitung newspaper reports that the suspect moved within the circle of an Islamist preacher, Ahmad Abdelazziz A, known as Abu Walaa, who was arrested in November.
A police notice lists six different aliases used by Anis Amri, born on 22 December 1992, who at times tried to pass himself off as an Egyptian or Lebanese.
The suspect was facing deportation as of June but there was a delay in receiving paperwork from Tunisia.