It turns out that the entire text of the book that Mel Gibson took as his inspiration for the movie is on line -- THE DOLOROUS PASSION OF OUR LORD JESUS CHRIST, by Anne Catherine Emmerich (1774-1824).

Tim Challies, in a site with the subtitle, "Putting the Fun in Fundamentalism," has catalogued many of the scenes in the film that Gibson took from Emmerich's book. From my brief glance at the book, it seems to me that a good deal of the horror film atmosphere comes from Emmerich's book (and certainly not from the Gospels).