Complex sentence: In 1999, journalist Rod Moran published a book "Massacre Myth" which reviewed the evidence and argued that Gribble had promoted and spread rumours of the alleged massacres and that many of the stories surrounding the events were fabrications by Gribble.
Split into simpler sentences: In 1999, journalist Rod Moran published a book "Massacre Myth" which reviewed the evidence arguing that there was no credible evidence that there had been any massacres and that Gribble had promoted and spread rumours of the alleged massacres. Moran argues that many of the stories surrounding the events were fabrications by Gribble.