This is... disappointing. There's a lot of buildup and a very emotional climax, but there is no resolution. Was the corridor sealed to conceal the murder? If yes, then why is the grandfather getting out of it freely? Hiding something like that should be a huge deal. There's no investigation, to consequences, we're told there was a burial and that the case served as a motive, but how? Why would the manager decide to do a copycat murder after so many years? How did he even know about it? Was he working there back then? Did he want to bring it to light? And then you have the characters. What's the point in showing them accidentally conceal the traces? It's not even good comedy. Why show them get that revelation if it doesn't actually mean anything for them, and even worse, for their relationship with their grandfather? You'd think they'd be angrier that their beloved grandpa screwed them up. And that he'd worry about all that being found out. Nah, nothing, nada, zero, you get a three-page epilogue that's anticlimatic for the sake of comedy, maybe, except it doesn't even deliver on that front.
It feels like it was supposed to be a longer story, but got cut short for some reason. What a shame.