Read around the late '70s to early '80s, could be from earlier. Could be a variation on the Judge Crater disappearance story, or just namedropped him. A man disappears walking on a crowded street. Then an unrelated case of another person disappearing... eventually the whole thing winds up in some kind of punchline, which I forget. It had third-person reportorial style: facts and dates are given, but the manner is a bit facetious, like the entries in The Hitchhiker's Guide to the Galaxy. It isn't "The Men Who Murdered Mohamed", either.