There are doubts that a Pakistani suspect in police custody is the driver of the vehicle that ran through a crowded German Christmas market, police chief Klaus Kandt says.
"It is in fact unclear whether (the suspect) was the driver," Kandt said during a press conference in response to a journalist's question on Tuesday.
The attack saw a large truck plough through a crowded Christmas market in western Berlin late Monday, leaving 12 people dead and dozens injured.
A man later identified as a Pakistani man who registered for asylum in Berlin earlier this year was detained near the scene shortly after the incident.
He has denied involvement in the attack.
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"We've got the wrong man and therefore a new situation. The true perpetrator is still armed, on the loose and can do fresh damage," German newspaper Die Welt cited a police official as saying.
Reuters reported Berlin police saying on Twitter that they were being vigilant as the suspect had denied involvement in the incident, which police have said was a deliberate attack.
Another suspect, a Polish national who was a passenger in the truck, was found shot dead at the scene.
Interior Minister Thomas de Maiziere said earlier that the gun had not been recovered.
