Other mistake: Joséphine Jobert is a Sergeant (the commissioner introduces her as such at the end of the first episode), but in the end credits of all the episodes before she takes over for Camille Bordey and becomes officially a Detective Sergeant, she is merely credited as "Officer Florence Cassell." By comparison, Fidel was credited as "Sergeant Fidel Best", even not being a DS.
Episode #4.4 - S4-E4
Other mistake: On the first day of investigations, Florence says that "two days ago" the victim withdrew a large sum of money. A CCTV shot is shown later in the episode, establishing that day as March 9th 2015 - remarkably consistent with the date of the previous episode and the coroner's report. So it is the 11th, and the investigation concludes on the 12th, a Thursday. However, at the end of the episode, Dwayne says that it's Saturday.
Episode #4.7 - S4-E7
Other mistake: Spoiler: While unmasking the culprit, Goodman never explains what happened to the real Dominic Claydon. Only that the perpetrator used his identity to get what he wanted.
