I notice with season 4, the murderers are caught by incriminating themselves in each episode. It seems to be very strong in this season. I wonder if it was written as a theme for the season?

Exercise in Fatality: alibi incriminates him
Negative Reaction: picks out the murderer's camera
By dawn's early light: place himself at crime scene
Troubled Waters: planting evidence
Playback: security system used to set up alibi incriminates him
A deadly state of mind: incriminates himself by identifying a person who was near the crime scene.