WARNING! This article contains SPOILERS for Dexter: Original Sin season 1, episode 8!Showtime’s Spencer himself being said killer, Miami Metro has also been investigating a string of connected NHI deaths. After trying to question a psychiatrist connected to those deaths, Harry and LaGuerta discover he was murdered, which leads them to the real serial killer.

In Original Sin season 1, episode 2, a man is found murdered and Spencer suspects it’s an NHI death, which Batista explains stands for “No Human Involved,” though the label refers to drug dealers, sex workers, and homeless people. A few more bodies appear that LaGuerta and Dexter believe are connected, with Dexter analyzing the crime scenes and assessing that the perpetrator is new, savoring his kills, and “trying out” different techniques. While investigating, Dexter is nearly hit by a familiar vehicle from Dexter season 1, leading to fan theories that the NHI Killer is actually the Ice Truck Killer.

Dexter: Original Sin Season 1 Episode 8 Confirms The Theory That Brian Moser Is The NHI Killer

Dexter's Biological Brother Is Original Sin's NHI Killer

While it might have seemed far-fetched for Original Sin to make one of its first big serial killer villains a younger version of a character from Dexter, that’s exactly what happened. Not only that, but Original Sin season 1’s serial killer is the killer from Dexter season 1, who was already being featured in a different timeline all throughout the prequel series. As it turns out, the NHI Killer in Dexter: Original Sin is none other than the Ice Truck Killer, aka Dexter’s biological brother Brian Moser.

Though Dexter: Original Sin’s main timeline takes place in 1991, the prequel has also intermittently woven in flashbacks to 1973–1974 when Dexter’s mother Laura Moser began working as a CI for Harry Morgan and the two started an affair. During those flashbacks, Original Sin has given a deeper look into the lives of younger Dexter and Brian Moser, with Dexter being a sweet and kind kid while Brian was already exhibiting troubling behavior prior to his mother’s death. While Harry was thinking back to this time, he had no idea that Brian was the killer he was looking for.

In Dexter: Original Sin season 1, episode 8, LaGuerta and Harry dig through the psychiatrist’s files in Tampa, as they believe that the NHI Killer is one of his patients. Harry eventually stumbles upon the file of Brian Moser, which reveals that he had recently been discharged from the psychiatric hospital but had several notes about disorderly conduct and his history of violence. After realizing that Raul Martinez, one of the NHI Killer’s victims, was Brian’s attending nurse at the hospital, Harry put the pieces together and realized that both of Laura’s sons had become serial killers.

How Dexter: Original Sin Season 1 Subtly Set Up Brian Moser's Killer Return

The Ice Truck Brian Used Appears In Episode 6

Even if he hadn’t turned out to be the NHI Killer, Original Sin season 1 already laid out some clues that Brian Moser was near Miami and would soon begin killing. In episode 2, a young man who seemed just a few years older than Dexter, wore Brian’s same style of clothing, and had a striking resemblance to Brian approached Dexter at a restaurant and asked about a seat at his table. Dexter was oblivious and said he was saving it for friends, but that moment teased the possibility for Brian to try reuniting with Dexter in their early 20s.

In Dexter: Original Sin season 1, episode 6, an even bigger Ice Truck Killer Easter egg was laid when Dexter is following Levi Reed. At one point during his pursuit, Dexter is separated from Levi when a refrigeration truck pulls onto the road between them. This truck is the same make, model, and design as the one used by Brian in Dexter season 1, including the same lettering on the back of the vehicle for “Miami Chills Ice.” It’s unclear whether Brian is already using this truck, but it was certainly a clue to his presence in the 1991 timeline.

Why Harry Hides His Discovery About Brian Moser

Harry Hides The Truth Out Of Guilt And Fear

Though Harry is now certain that Brian Moser is the NHI Killer, he doesn’t tell LaGuerta about it. Part of the reason Harry hides the truth about Brian is that he feels guilty about what happened to Laura and that he adopted Dexter but not Brian. He feels partially responsible for what Brian became, and his immediate reaction is that he should figure out what to do with Brian before Miami Metro gets involved. Additionally, Harry knows that it might lead to his affair with Laura Moser and history with Dexter before the Shipping Yard Massacre coming to light.

Camilla, Bobby, and Captain Spencer would already be aware of the truth about Dexter's background in Original Sin.

Brian being exposed would not only lead to Dexter finding out the truth about what happened to his mother and brother, but also Dexter’s dark history being revealed to the rest of the station – which Harry carefully had Camilla scrub from files before Dexter: Original Sin. Since Brian became a killer after Laura’s murder, Miami Metro might also suspect that Dexter could be a killer as well, which would lead to deeper investigations into his life and potentially expose Dexter’s crimes and the Code of Harry.

New episodes of Dexter: Original Sin season 1 release Fridays on Paramount+ with Showtime.