Germany's Chief Federal Prosecutor has released a man arrested after a truck attack on a Berlin Christmas market that killed 12 people.
Police had arrested a Pakistani asylum-seeker, but said he may not be the attacker and the real perpetrator could still be on the run.
The prosecutor's office said he had now been released as there was not enough evidence to pursue a case against him.
The truck smashed into wooden huts serving mulled wine and sausages at the foot of the Kaiser Wilhelm memorial church, one of west Berlin's most famous landmarks, at about 8pm on Monday. Forty-eight people were injured, 18 severely.
The Pakistani man was captured in a park after reportedly fleeing the scene. He had denied involvement.
The 23-year-old arrived in Germany from Pakistan at the end of last year.
Federal prosecutor Peter Frank said the style of attack and the target suggested Islamic extremism.
News of the man's arrest had led politicians in Germany and beyond demanding a crackdown on immigration.
Chancellor Angela Merkel told reporters: "There is much we still do not know with sufficient certainty but we must, as things stand now, assume it was a terrorist attack."
She added: "I know it would be especially hard for us all to bear if it were confirmed that the person who committed this act was someone who sought protection and asylum."
Berlin police tweeted that they were "particularly alert" because of the arrested man's denial of any involvement.
Die Welt newspaper quoted an unnamed police chief as saying: "We have the wrong man. And therefore a new situation. The true perpetrator is still armed, at large and can cause fresh damage."
The truck belonged to a Polish freight company and its rightful driver was found dead in the vehicle. Interior Minister Thomas de Maiziere said a pistol believed to have been used to kill him had not yet been found.
German media said the arrested man had jumped out of the driver's cab and run down the street towards the Tiergarten, a vast park in central Berlin. Several witnesses called police, including one who chased the suspect while on the phone, constantly updating officials on his whereabouts.