: By analyzing the different patterns and ages of the wallpaper layers, the BAU is able to establish a timeline for the murders, which they find date back over 20 years.
In the context of the episode " Starter Home " (Season 14, Episode 2) , the "paper" you are likely referring to is the wallpaper that serves as a central piece of forensic evidence . [S14E2] Starter Home
: The killer's signature involves a specific ritual related to the home's renovation and the application of new wallpaper each time a new victim was added. : By analyzing the different patterns and ages