The suspect’s identity papers were found inside the cabin of the truck used in Monday’s attack, which left 12 people killed and 48 injured, the official said. The man was born in 1992, he said.
An urgent manhunt is underway for the suspect, who is potentially armed and dangerous, before he can strike again, CNN terrorism analyst Paul Cruickshank said.
Authorities on Tuesday released another man who was arrested shortly after the truck smashed into the market, saying there was no evidence to connect him to the attack.
Police have appealed to the public for any digital videos and photos they have of the attack or possible suspects. They tweeted Tuesday they were investigating 508 leads.
ISIS claimed it had inspired the attack. The terror group’s affiliated Amaq News Agency described the perpetrator as a “soldier of the Islamic State” who had acted in response to calls for attacks in the West.
German police said they are treating the attack as terrorism, but there is no evidence of a direct link with ISIS.
However, another German security official told CNN that investigators believe the Tunisian suspect is linked to a pro-ISIS network operating in Germany.
The main figure in the network, Ahmad Abdulaziz Abdullah — a 32-year-old Iraqi national also known as Abu Walaa — and four others were arrested and charged with terrorism offenses in November.
German federal prosecutors said then that Abdullah was the ringleader of a multiregional recruitment network. The group allegedly targeted and radicalized young Muslims in the northwestern states of Lower Saxony and North Rhine-Westphalia.
On Tuesday evening, police released an asylum-seeker believed to be from Pakistan who had been detained in the immediate aftermath of the truck attack. According to German witness media, witnesses had said he had been driving the truck.
But Peter Frank, general prosecutor at Germany’s Federal Court of Justice, said that forensic tests offered no link between the man and the truck’s cabin.