How does the author use flashback in the novel, The Widow?

The author employs flashbacks throughout the story and relates each chapter focused on a different character. For example, Chapter 4 is written in the perspective of The Widow on June 9, 2010; Chapter 5 is focused on the perspective of the Detective on October 2, 2006; Chapter 6 is related from the Widow's perspective on June 9, 2010; and Chapter 8 follows the Reporter’s perspective on October 11, 2006.