The 40-year-old was allowed to walk free on Thursday, after German authorities determined that he was not a "possible contact person for Anis Amri," spokesman Frauke Köhler told reporters on Thursday.

The man was detained a day before, after the authorities found his phone number stored in Amri's cell phone, which had been found at the scene of the Berlin attack.

On December 19, the 24-year-old Tunisian citizen Amri drove a truck through a Christmas market in central Berlin, killing 12 people and injuring 48. He is also believed to have killed the Polish driver of the truck he used. Contrary to some reports, the authorities discovered no knife wounds on the body. Preliminary info suggests that the 37-year-old Polish national died close to the time of the attack. However, the full autopsy results are expected only in January.

The "Islamic State" militia claimed responsibility for the terror strike.

Investigators also retrieved a .22 caliber bullet from the cab of the truck. The caliber matches the weapon Amri used in the shootout with the police in Milan. The ballistic experts are currently performing tests to confirm the same gun was used in both incidents, Köhler said.

Video of Amri authenticated

She also confirmed earlier reports that the Berlin rampage was cut short due to a braking system in the truck, which was programmed to stop the vehicle in the case of a collision.

"We assume that the truck stopped after 70 to 80 meters (yards) due to its automated breaking system," preventing an even larger tragedy, Köhler said.

The spokesperson also confirmed that a video in which Amri is seen pledging allegiance to Islamic State was authentic.

"We are coming to slaughter you, you pigs," Amri says in the apparently self-made video.

German authorities are continuing their search for other suspects and accomplices.

Also on Thursday, Italian police searched three houses in and around Rome where Amri may have spent time, a judicial source said.

German authorities also managed to reconstruct parts of Amri's escape route from Berlin to Milan, based on a SIM phone card and a train ticket found on his body. Amri apparently traveled to Dutch city of Nijmegen, not far from the German border, where a company had been distributing those phone cards for free.

Dutch sources also confirmed that man who looked like Amri was caught by surveillance cameras in Nijmegen. From there, Amri reportedly took a bus to France.

Italian officials also found Amri's train ticket from the French city of Lyon to Milan in northern Italy.

dj/kms (dpa, AP, AFP, Reuters)