Which of the two versions
Mr.S. was found murdered, by John
Mr.S. was found, murdered by John
means that John found the body and which one means that John was the murderer?
The first version has at least three meanings: John found the body; John did the murder; someone found Mr S murdered and lying at the side of John (we don't know if John was dead too, or merely lying there).
The second simply means that the murdered body was found and that John did the murder.