German officials admit - they arrested the wrong man. ISIL says it was behind the truck attack on a Berlin market that killed 12 people. If true, it's the "first mass casualty attack by Islamic extremists" on German soil.

Flowers and candles are placed to mourn the victims of the attack at a Christmas market in Berlin, capital of Germany, on Dec. 20. 2016. At least 12 people were reportedly killed and many others injured after a tractor-trailer truck ploughed into a crowd at the Christmas market in Berlin on Monday night. (Xinhua/Shan Yuqi)

Berlin is mourning its dead. Ploughed down as they celebrated - yards from the Memorial Church.The German Chancellor paid tribute here early on Tuesday afternoon. Angela Merkel talked of 'results'.

German Chancellor Angela Merkel speaks during a press conference in Berlin, capital of Germany, on Dec. 20, 2016. "We must assume it was a terrorist attack," Germany Chancellor Angela Merkel said here Tuesday, referring to an attack at a Christmas market in Berlin on Monday night that killed 12 people and injuring many others. (Xinhua/Shan Yuqi)

Merkel said, "According to the present results of our investigation, we have to presume a terrorist attack. Even if it is very difficult, we will find the strength to live the life that we want in Germany, in a free, united and open society."

That was after special forces raided a refugee shelter at the old Tempel of airport - the temporary home of a 23-year- old Pakistani asylum seeker arrested on Monday night.

The emerging narrative seemed clear-cut until: "We don't know for certain whether there is one or several perpetrators. So far we don't know for certain whether he or she had supporters."

"This investigation is not yet complete. We must get used to the idea that the arrested Pakistani national was possibly not the perpetrator or that he didn't belong to the group of perpetrators."

That was soon confirmed with his release on grounds of insufficient evidence. The actual perpetrator is reportedly believed to have shot the original Polish driver in the head. Leaving nervous Berliners with many questions about an investigation that's been turned upside down.

Whoever's responsible seems to be on the loose, possibly armed - and perhaps has help because now Islamic State say they are behind this attack. Authorities are warning there's a significant risk of another incident.