To play devil’s advocate for a moment, there are precedents to suggest that the smell from inside a sealed wall might not tip people off immediately.
In the infamous case which led to the abolition of capital punishment in Great Britain, a man was executed for the murder of his wife. They had lived in a duplex. Some time later the other resident of the duplex moved out, and ment hired to do rennovation work discovered that a wall in his apartment was stuffed with the bodies of women he had murdered.
Similarly, John Wayne Gacy seems to have gotten by with keeping bodies in his crawlspace for a long while without the neighbors taking notice.
Then there was the Dahmer case. In that instance neighbors had been much offended by the odor, but said they thought he was plucking chickens. That struck me as one of the most incredible aspects of that case; that people would think their neighbor was plucking chickens in large quantities and not complain about the stench.
Years ago I inspected a chicken rendering plant. At the end of my tour I asked the manager how long it took to get used to the smell. “Four years” he instantly replied. I thought it was odd that he had such a prompt, exact answer. He then explained that long-time employees invariably found that their capacity to smell anything had rotted away completely by the end of four years.
The Jarrott Mansion in Cahokia is said to be the oldest brick house still standing in Illinois. When it was converted into a historical museum in the late 1970s workmen found a horse’s skull inside a wall. Nobody ever did figure out what that was about, though there was suspicion that it had something to do with some kind of Native American ceremony. Of course, the skull might have been clean of flesh when it was sealed up. Then again, a friend of mine who rennovated a house in Elsah, Illinois (an old Christian Science settlement), lived in the house for years before he found the remains of a large snake in a wall.
On the other hand, I just did a quick search for “Nemo” using Google. I came up with 86 pages. Scanning the results here and there, I came up with lots of citations for Captain Nemo and Little Nemo in Slumberland, but only one real individual named Nemo–and he was a dog.
Yeah: I suspect it is a legend.