The Mystery of the Yellow Room - S1-E8
Plot hole: The resolution of the case hinges on the fact that the titular room had a door that was then sealed off completely by order of a certain character. The key word here is "order"; the culprit did not do it by their own hand, they ordered other people (normal White House staff being asked to perform normal work) to get it done, without even overseeing the operation. They did it to conceal an incriminating object that was inside the closet that was being sealed. No worker (or team of workers, working in a historical building such as the White House, even) in their right mind would wall up a closet without first opening it and making sure it was empty. From the culprit's perspective, they directed a crew of people towards the place where the very conspicuous, incriminating, bloodied evidence was hidden and just assumed nobody would carry out due diligence. And it worked.