Fabrice Du Welz began the century as a master of Belgian gothic, riding the wave of Euro-extreme cinema. Calvaire, or The Ordeal, from 2005, was a gruesome gripper. Since then, in a chequered career, he has more or less maintained his stride, and now he comes to Venice as director and co-writer of an initially promising true-crime horror procedural. It is loosely inspired by the serial killer and child rapist Marc Dutroux, whose case enraged the Belgian public when it became clear the country’s various quarrelling law-enforcement authorities, hampered by bureaucracy, incompetence and turf-war disputes, had in effect allowed Dutroux to go free for years.

It’s an intriguing premise and this baggy, free-ranging movie presents a tonal range of sour acrimony, anxiety and occasional flourishes of nauseous black comedy. But it’s a long film which finally – and rather perfunctorily – voyages into the murky waters of deep-state conspiracy, and the drama doesn’t really have the rhetorical resources or the performances to make that case plausibly or interestingly.