 FACT: SPOILER: At some point in the movie, it is revealed that the  actual book written by Walter Sparrow was written in 1991. There is  one scene where he is reading the book and reading off dates of evil  occurrences that add up to 23, and one of those dates is the  Oklahoma City bombing, which happened in 1995. Since he is reading  from the book that he wrote in 1991, that bombing would not have  occurred in time to be included in the book.