YMMV / Numb3rs S 05 E 21

• Complete Monster: Robert Posdner is a stealth predator who changes victims, methods, and even locations to avoid leaving a clear pattern, while also killing anyone who might have seen him. Posdner's murders started approximately 20 years before the episode, in high school, when he stalked and killed a fellow student who rejected him, before threatening the girl's then-boyfriend. All in all, Posdner is responsible for at least 4 onscreen murders, attempts to murder a couple, can be tied to a few more, and has a Trophy Room linking him to potentially many, many more. Liz even states afterwards that she intellectually understands how sociopaths become serial killers but this guy just seems evil.