The only suspect held after Monday's deadly lorry attack on a Berlin Christmas market has been released due to lack of evidence to pursue the case against the man, BBC reports quoting prosecutors.
The suspect was identified by media only as Pakistani national Naved B. But the suspect has denied involvement.
Officials earlier suggested that a perpetrator or perpetrators might be on the run.
Meanwhile, the death toll from the deadly lorry attack has risen to 12. Initially nine people were reportedly killed and 49, said German police.
Before the man was released late on Tuesday, German officials said they could not be be sure if he was involved in the attack.
"We have to entertain the theory that the detainee might possibly not have been the perpetrator," federal prosecutor Peter Frank told reporters.
The style of attack and the target suggested Islamic extremism, he said.
The man, 23, was captured in a park after reportedly fleeing the scene.
He is believed to have been known to police for minor crimes, but had no links to militant organisations.
He arrived in Germany on 31 December last year and his asylum application was still in progress.
The usual driver of the lorry, Polish citizen Lukasz Urban, was found dead on the passenger seat of the lorry, reportedly with gunshot and stab wounds to his body. No gun was recovered.
German Chancellor Angela Merkel has vowed to punish those responsible for the attack "as harshly as the law requires".
Her open-door policy on migration, which saw 890,000 asylum seekers arrive in Germany last year, has divided the country, with critics calling it a security threat.
For Angela Merkel the legacy of the Berlin attack will be political.
It is not clear who the perpetrator was. But if it proves to be someone who came as a refugee she will face more pressure.
She has stuck to her welcoming policy towards refugees fleeing war and persecution, and a majority of Germans have continued to back her.
But Merkel's political opponents, notably the far right Alternative fur Deutschland (AfD), have attacked her again following the Berlin attack, saying she has compromised Germany's security by letting in people without knowing who they are.
It is a charge they will seek to press as Germany gears up for federal elections next year.
The AfD had surged in regional elections this year. But Germany's main parties have all said they will shun any question of sharing power with the AfD.
And Angela Merkel has seen her support rise in recent polls. It is why the issue of who carried out the Berlin attack is vital for Merkel and her vision of a free, open Germany.
Merkel has expressed concern that the attacker might turn out to be an asylum seeker.
"I know that it would be particularly difficult for us all to bear if it turned out that the person who committed this act was someone who sought protection and asylum in Germany," she said.
The co-leader of Germany's anti-immigration AfD party, Frauke Petry, blamed Merkel's liberal policy on migrants.
"The milieu in which such acts can flourish has been negligently and systematically imported over the past year and a half," she said.
Horst Seehofer, the leader of Merkel's sister party in Bavaria, urged the chancellor "to rethink our immigration and security policy and to change it".