Top 3 Popular Fan Theories About Characters in Dexter: Original Sin That Were Completely Wrong

People speculated, but they were wrong. Let’s dive into those theories.

The first season of Dexter: Original Sin, the highly anticipated prequel series set in 1991 Miami, has officially concluded its 10-episode run. Spanning two months from December 13 to Valentine's Day, the series reintroduced fans—both old and new—to younger versions of beloved (and sometimes not-so-beloved) Dexter characters, all wrapped in an authentic early ‘90s aesthetic.

Beyond the familiar faces, Dexter: Original Sin also introduced several brand-new characters never mentioned in the original series. Many of these fresh additions were part of Miami Metro PD, including Captain Aaron Spencer (Patrick Dempsey), Tanya Martin (Sarah Michelle Gellar), and Bobby Watt (Reno Wilson). While we now know the fate of Captain Spencer, the futures of Tanya and Bobby remain a mystery. Given that neither of them appears in the Dexter timeline starting in 2006, their absence raises major questions—did something happen to them, or did they simply leave Miami Metro?

Throughout the season, fan theories ran wild across the internet, speculating on hidden motives, shocking twists, and secret identities. However, as it turns out, many of these theories were way off the mark. The show’s writers masterfully misled audiences, making certain characters appear more suspicious than they actually were.

Now, let’s break down the top three fan theories that turned out to be completely wrong—plus a bonus one that had fans convinced!

1. Tanya Martin Was Hiding Something or a Secret Villain

One of the biggest fan theories revolved around Tanya Martin, Miami Metro’s forensics chief, played by Hollywood icon Sarah Michelle Gellar. Given Gellar’s status as a ‘Special Guest Star’ and her massive fanbase from Buffy the Vampire Slayer, many assumed she was being set up as a major antagonist.

In Dexter’s history, ‘Special Guest Stars’ often play the season’s primary villain (e.g., John Lithgow’s Trinity Killer). However, this isn't always the case—Julia Stiles in Dexter Season 5 and Charlotte Rampling in Dexter Season 8 played key roles without being villains.

As Season 1 progressed, fans noticed that Tanya Martin was underutilized, which led to rampant speculation that she was secretly the NHI Killer or an accomplice to Captain Spencer, the confirmed child kidnapper. Subtle behaviors and misleading clues fueled these suspicions, but in the end, Tanya turned out to be a perfectly normal, law-abiding character. Her limited role may have felt like a missed opportunity, but it also kept viewers guessing.

Now, the big question remains: what’s next for Tanya in a potential Dexter: Original Sin Season 2?

2. Gio Was Hiding a Sinister Secret

Another popular theory involved Gio, played by Isaac Gonzalez Rossi, who was introduced in Episode 4, Fender Bender. Deb met him at a nightclub, and their relationship escalated quickly—almost too quickly. Given Deb’s historically bad luck with men (looking at you, Brian Moser!), fans immediately suspected Gio was up to no good.

Initially, some theorized that Gio was the child kidnapper. When that theory was debunked, others speculated that he was the NHI Killer or even the secret son of Hector Estrada (Carlo Mendez) due to their physical resemblance.

The reality? Gio was just a wealthy playboy cheating on his fiancée while dabbling in drugs. His only crime was being a terrible boyfriend to Deb. The writers played with audience expectations, even placing a golden cobra statue in Gio’s kitchen—a detail eerily similar to the symbol of Estrada’s cartel—purely as a red herring.

Gio was nothing more than a distraction, proving that not every new character hides a dark past.

3. Harry Morgan Would Be Killed by Brian Moser in Episode 10

Perhaps the most dramatic fan theory suggested that Harry Morgan (Christian Slater) would meet his demise at the hands of Brian Moser in the Season 1 finale, rewriting Dexter history by proving that Harry never actually took his own life.

This theory gained traction after it was revealed that Brian was carrying out the NHI murders as revenge. Many fans speculated that he would target Harry next, creating a shocking twist.

However, there was a major flaw in this theory—Harry’s death timeline was already established in the original series. According to Dexter, Harry died one year after leaving the hospital following a health scare. Showrunner Clyde Phillips even confirmed in interviews that keeping Harry alive for future seasons was a priority, as his father-son dynamic with Dexter is central to the show’s direction.

The Season 1 finale, Code Blues, put this theory to rest. Harry is still alive… but for how much longer?

Bonus Fan Theory: Bobby Watt Would Die After Being Shot

A fan-favorite character, Bobby Watt (Reno Wilson), faced a life-threatening situation in Episode 8, Business and Pleasure, after being shot in the neck during a cartel raid. Given that Bobby is not present in Dexter’s main timeline, fans assumed he wouldn’t survive Season 1.

The show played into this fear, dropping hints and foreshadowing lines that suggested Bobby’s death was inevitable. Miami Metro even organized a blood drive to help save him, further heightening the tension.

However, in a surprising twist, Bobby survived! Fans cheered as he walked out of Angel of Mercy Hospital, proving that not every tragic prediction comes true.

Final Thoughts: Did You Fall for Any of These Theories?

These were just some of the many fan theories that kept audiences engaged throughout the 10-episode run of Dexter: Original Sin. The showrunners successfully misled fans, creating suspense and intrigue at every turn.

Did you believe any of these theories? Which ones had you convinced? Share your thoughts in the comments below!