It appeared that something was amiss when the Berlin police tweeted this early in the morning U.S. time:

The temporary arrested suspect denies the offense.
Therefore we are particulary alert.
Please be also alert.#Breitscheidplatz

— Polizei Berlin Einsatz (@PolizeiBerlin_E) December 20, 2016

That suspect has already been released. Berlin police posted a fuller explanation for that decision on their website (via Google Translate):

The accused who had been temporarily arrested on the occasion of the attack on the Berlin Christmas market on 19 December 2016 was released in the evening on the orders of the Federal Prosecutor. The previous investigations did not result in an urgent offense against the accused. He made extensive statements in a police hearing but denied involvement. A complete tracking of the truck driver after the performed stop is not done by eye witnesses. The criminal investigations carried out so far have not been able to prove a presence of the accused during the incident in the cab of the truck.

NBC News has a bit more detail:

Germany’s chief prosecutor Peter Frank echoed that, warning: “We must get used to the idea that he was possibly not the perpetrator or that he didn’t belong to the group of perpetrators.” He added: “We do not know if there were more people involved in a support role.”

In other words, the attacker may have escaped and may not be acting alone. There was also some more information on the other man found dead inside the truck’s cab:

Among the dead was a Polish man found shot to death inside the cab of the stolen truck. The weapon has not been found.

Bloodstained clothing was also found inside the cab, but the suspect in custody was wearing clean clothes, Frank said.

The truck itself came from Poland and the owner said he was concerned it had been hijacked because he hadn’t been able to reach the driver. So it appears the attacker hijacked the truck while the Polish driver was at the wheel and, at some point, killed him.

If police got the wrong man last night that means the attacker who murdered 12 people and injured dozens more has had quite a few hours to run. Assuming he had some sort of escape plan and documents, he could have crossed into any number of other countries by now.

But the really worrisome possibility is that he didn’t run but is only in hiding as he waits for a chance to strike again. If you’re willing to die in the effort to murder innocent people why would you run? There are plenty more trucks to hijack at gunpoint and plenty more public markets to attack.

This Euronews report points out that police with machine guns will be guarding outdoor markets and barriers are being set up in some German cities. But until the attacker is captured, police and citizens should assume this isn’t over.