As the shellshocked German capital reeled from the country's deadliest attack of recent years, doubts emerged over whether the man detained overnight actually committed the atrocity.
Berlin's police chief, Klaus Kandt, said "we may have a dangerous criminal in the area", and announced that security would be boosted while urging "heightened vigilance".
Prosecutor Peter Frank also said "we may have to get used to the idea that the detained man may not be the perpetrator", while forensic work and questioning continued and investigators asked the public to send them any photos and video footage.