Chancellor Angela Merkel decried Monday’s assault — in which a truck carrying a payload of steel plowed into festive stalls and fairgoers in Berlin, leaving 12 dead and dozens injured — as a presumed “terror attack,” even as German police scrambled to find the culprit. The only suspect so far — a Pakistani asylum seeker taken into custody shortly after the bloodshed — was released by police Tuesday because of insufficient evidence.

Late Tuesday, the Islamic State, through the affiliated Amaq news agency, claimed that the attacker was a “soldier” responding to its call to target nations fighting the group in Iraq and Syria. The Islamic State has wielded the term before to describe lone wolves inspired by its rhetoric, and its level of involvement, if any, in coordinating the attack remained unclear.

In Germany and across Europe, revulsion and angst over the strike at a symbol of the region’s Christmas traditions sparked governments to act. The holiday spirit was being replaced by muscle.

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