That’s a classic study where people are told there’s a fire in a warehouse, and we found oil paints or flammable materials in the wiring cabinet. Then, later on, it will say, by the way, the wiring cabinet was empty. Now, if that's all you do, people will still think that there was oil paint in the wiring cabinet. Just simply saying something isn't true doesn't do the trick.
But instead, if you say the wiring cabinet was empty, and we found some petrol-soaked rags [elsewhere] at the scene, then people forget about the wiring cabinet because they have an alternative explanation for the fire. You need an alternative to let people let go of the initial information.