All of this is based on a conspiracy theory that John Paul I, who was pnly pope for about a month was indeed poisoned. At the time he took over, there was a huge scandal at the Vatican bank and it was moxed up with some crooked European businessmen, one of whom hanged himself from a bridge in London with a satchel of money (as is depicted in GFIII). The archbishop in charge of the Vatican Bank was an american, and the Gilday character is based on him.