An 18-year-old male driving an off-road motorcycle died from complete decapitation when his motorcycle tore a roadblock chain from its attachment. The decapitation injuries of the head and the torso corresponded perfectly, without apparent loss of tissue. The severance plane passed horizontally through the upper cervical region and C4, which sustained a comminuted fracture. The sharply delineated severance edge had a band-like abrasion. The decapitation resulted from the rotational movement of the unstrung chain, which struck and strangled the driver’s neck. We were able to explain the movement of the chain and the decapitation mechanism. This case emphasizes the importance of discussing dynamics with experts to clarify a causal mechanism.