Investigators arrive at the scene of a warehouse fire. The building is completely destroyed. They observe the following: (1) the building's alarm system was disabled before the fire; (2) all external security cameras had been spray-painted over sometime in the preceding 24 hours; (3) a strong odour of gasoline pervades the rubble despite the building having no gasoline-powered equipment; (4) the building owner had recently doubled the insurance coverage on the property. A junior investigator suggests the fire was caused by faulty wiring in the old building. What single piece of physical evidence most directly contradicts the faulty wiring theory?