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The claim of the lorry attack in Berlin by so-called Islamic State (IS) does not prove much in terms of the attack. The group often refers to individuals who carry out attacks as its "soldiers" but the crucial question is firstly whether the individual had any form of direct contact with IS.

Face-to-face or online communication are possible but far from certain. If there was no direct contact, it could still be the case that an individual was inspired rather than directed by the group.

In this case, an individual may leave his or her own pledge of allegiance in written form or online or in a video.

But until such evidence emerges, it remains hard to know if this is just an opportunistic claim by the group rather than one based on real substance.