The invisible murderer in the shower is a person that's not actually a murderer, but just a Goomba that lives in a shower. Since he's invisible, Nobody can see him. He's called a murderer only because he spills Volvic Revive on people, which melts them. He's also known to be great friends with Luigi, after seeing him in the shame Luigi's Bathroom. It is rumoured that the goomba is invisible due to a curse that was laid on him by the evil wawawawawawawaboo (which of course makes him supremely evil), however due to the extremely long name, it is more likely to be the fault of Bill Gates, who sometimes likes to pretend to be a ghost, for some reason.