Complex sentence: Because people had begun to claim Garrett unfairly ambushed Bonney, Garrett felt the need to tell his side of the story and called upon his friend, journalist Marshall Upson, to ghostwrite a book for him.
Split into simpler sentences: Because people had begun to claim that Garrett unfairly ambushed Bonney, Garrett felt the need to tell his side of the story. In response, Garrett called upon his friend, journalist Marshall Upson, to ghostwrite a book for him.