How Robert really died.
From what's revealed, he once decided that "A man's got to do what a man's got to do", and that's what got him turned into a ghost. And in book 3, it's confirmed that he died via a bullet. Furthermore, he was a councilor in 1941... the year that Pearl Harbor was attacked.
Therefore, it is very likely he signed up for the military after the bombing, and died fighting in World War II.
