What is the author's style in A Very Long Engagement by Sebastien Japrisot?

This novel begins and ends with an omniscient point of view, telling us about the five condemned soldiers, giving the background of each, his reason for being where he is, and his state of mind. The rest of the book is told mainly from Mathilde’s point of view, but Mathilde receives most of her information through epistles and telegrams and interviews. In this way, the emotions and thoughts of the other characters are presented. While the reader has the pleasure of discovering clues to the mystery along with Mathilde, the author also uses these letters and interviews to round out each character.