Does "he should not have known" mean "he must not know"?
There are one or two points about the case which would bear discussion. One is that a man with so remarkable a name as Charles B. Rosma should never have been traced, considering all the publicity which the case acquired. This would certainly at the time have appeared a formidable objection, but with our fuller knowledge we appreciate how very difficult it is to get names correctly across. A name apparently is a purely conventional thing, and as such very different from an idea. Every practising Spiritualist has received messages which were correct coupled with names which were mistaken. It is possible that the real name was Ross, or possibly Rosmer, and that this error prevented identification. Again, it is curious that he should not have known that his body had been moved from the centre of the cellar to the wall, where it was eventually found. We can only record the fact without attempting to explain it.