A Pakistani man suspected of being the driver of a lorry that ploughed into a crowded Berlin Christmas market has been released.
The development means that the main suspect in the attack which killed 12 people is still on the loose.
A manhunt is now taking place to find the perpetrator who is believed to be armed.
German publication Welt earlier quoted officers as saying of the detained asylum seeker: "We have the wrong man.
"The real culprit is still armed, at large and can cause new damage."
It said police had not found the blood of a dead Polish truck passenger on the suspect.
The gun used to shoot the victim, who was the original driver and whose body was discovered in the cab, has not been recovered.
Witnesses described the truck ploughing through wooden huts serving hot wine and food, sending people flying.
Six of the dead from the attack have been confirmed as Germans while work goes on to identify the others.
Forty-eight people were also injured in the attack, 18 of them are in a serious condition.
The man who was arrested was reportedly named Naved B and arrived in Germany in December last year.
He was staying at a refugee centre in Berlin and was detained near the scene of the crash in Breitscheidplatz.
The owner of the company which operated the truck said Lukasz Urban, 37 - who was also his cousin - had been found stabbed and shot in the passenger seat.
He said he identified him from police photos. "His face was swollen and bloodied. It was really clear that he was fighting for his life," Ariel Zurawski told Polish broadcaster TVN.
Mr Zurawski said the lorry had gone to Berlin loaded with steel beams and that it must have been hijacked.
He described Mr Urban as a "good, quiet and honest person".
GPS data found several apparent attempts to move the lorry in the afternoon before the attack, Mr Zurawski told TVN.
Chancellor Angela Merkel, who laid white roses at the scene on Tuesday afternoon, said she was "shocked, shaken and deeply saddened" by the attack - one of a number in Germany this year.
Under her leadership the country has pursued a liberal policy on welcoming asylum seekers.
Security at 10 markets in Manchester has been increased after events in the German capital, and police in London are also reviewing arrangements for Christmas and New Year events.
It comes five months after 86 people died in Nice when a truck mowed people down on the French city's seafront.
Islamic State claimed responsibility for the attack.
This is a developing story...
