Tunisian man Anis Amri has been named as the prime suspect in the Berlin truck attack.
A manhunt is now underway across Europe.
Identification papers of 24-year-old were found in the cab of the truck that ploughed into a Christmas market on Monday.
Twelve people died and almost 50 were injured in the attack.
Police say Amri could be armed and dangerous, and security in Berlin has been increased.
A $150,000 reward is being offered for information leading to Amri's arrest.