Anis Amri had been considered a possible terror threat by the country's authorities before this week's crash
Germany has issued a reward of up to €100,000 to find the main suspect in the Berlin Christmas market attack.
A Europe-wide manhunt has been launched to trace Tunisian Anis Amri, who is believed to be armed and dangerous and has links to Islamic extremists, say investigators.
The 23-year-old is suspected of being at the wheel of a lorry which ploughed into a crowd of shoppers at a busy market in the German capital.
Twelve people were killed and 48 others injured in Monday evening's attack, which has been claimed by the Islamic State terrorist group.
Authorities have issued a European arrest warrant for Amri, who is thought to have used six different aliases and three different nationalities.
German website Bild said he was known to police.
Amri, who arrived in Germany in July 2015, had been considered a possible terror threat by the country's authorities before this week's crash, according to an official.
The interior minister of North Rhine-Westphalia state, Ralf Jaeger, said "security agencies exchanged information about this person in the joint counter-terrorism centre, the last time in November".
Mr Jaeger said state police had launched proceedings against Amri on suspicion that he was preparing a serious crime.
He said Amri had been in contact with the network of a leading Islamist ideologist known as Abu Walaa.
Mr Jaeger also said German authorities rejected an asylum request by Amri in July.
They prepared to deport him but were not able to do so as he did not have valid identity papers, he said.
The reward has been offered for information leading to the suspected driver being detained.
Documents which were apparently asylum office papers issued to Amri were found in the truck cab, according to German media.
He is described as being of average height and weight, with black hair and brown eyes.
Tunisian anti-terror police have questioned his family following the attack.
The original driver of the lorry, Lukasz Urban from Poland, was beaten and stabbed before his vehicle was driven by a hijacker at the market in Breitscheidplatz, it is believed.
Mr Urban, 37, was still alive during the rampage and was then shot dead just before the attacker fled the scene, according to reports.
A Pakistani asylum seeker who was arrested shortly after the massacre was released by police on Tuesday due to lack of evidence.