A dark theory about the mystery killer in Dexter: Original Sin seems very plausible after a 2023 horror movie starring the possible murderer. The mystery of who killed Jimmy Powell in Dexter: Original Sin is shaping up to be the show’s biggest twist. There are only a handful of new characters in the cast of Dexter: Original Sin, which means there are only a few potential killers so far. Since characters like Angel Batista (James Martinez) and Maria LaGuerta (Christina Milian) are still around in the original Dexter, there’s no way they could have killed Jimmy Powell.

Most of Dexter‘s serial killers also have some kind of personal connection to Dexter Morgan (Patrick Gibson), so it seems likely that Jimmy’s killer is already in the show. Even though there aren’t many possibilities for who could have killed Jimmy, his death remains a mystery even after the ending of Dexter: Original Sin episode 5. Now, however, a new fan theory may have cracked the case and exposed Jimmy’s killer hiding in plain sight. The theory also seems very likely thanks to a completely separate horror film starring the same actor.

Aaron Spencer Is Dexter: Original Sin Season 1’s Secret Villain – Fan Theory Explained

Captain Spencer Had The Means, Time, & Knowledge To Kill Jimmy Powell

The person who killed Jimmy Powell may be hiding in plain sight in Dexter: Original Sin, as a new theory asserts that it was Captain Aaron Spencer (Patrick Dempsey). Several Reddit users, like Shmullus_Jones, have hypothesized that since Spencer isn’t in the original Dexter, and since his job as the captain of Miami Metro Homicide effectively rules him out of any investigation, he could have kidnapped and killed Judge Powell’s son. The theory holds some water, as Spencer likely knew the Powells and could have easily convinced Jimmy to come with him, but there’s even more to the idea than that.

As Dexter: Original Sin episode 4 showed, Spencer is still quite angry about his wife’s infidelity and their divorce. He’s also been mostly absent in his son’s life, which means Spencer has ample time outside of work to moonlight as a killer. Plus, his knowledge of law enforcement would make it extremely easy for Spencer to confuse the detectives of Miami Metro and put them on the cartel’s scent. If Spencer does prove to be the killer, it would also present a great moment of drama and tension between Harry (Christian Slater) and Dexter as the latter tries to convince his father to let him kill Spencer.

Patrick Dempsey’s Killer Reveal In Thanksgiving Makes The Spencer Villain Theory More Likely

Dempsey Already Played A Cop-Turned-Killer In Thanksgiving, & He Could Do It Again In Dexter

There’s another piece of evidence that suggests Captain Spencer could be the killer in Dexter: Original Sin. In 2023’s Thanksgiving, Patrick Dempsey played Sheriff Eric Newlon, who turned out to be John Carver, the movie’s killer. The twist of Newlon’s true identity was so shocking, and Dempsey played both the law enforcement and murderer sides of his character so well, that he could easily do it again in Original Sin. It’s even possible that Thanksgiving served as a sort of proof of concept for Dempsey to be cast as both a police captain and a serial killer in Original Sin.

Spencer Being Original Sin’s Killer Could Help Solve A Missing Dexter Character Mystery

Captain Matthews Is Strangely Absent From Original Sin – Spencer Being A Killer Could Bring His Character In

Perhaps the best part of Captain Spencer being the killer in Dexter: Original Sin is how well it would explain one noteworthy character’s absence. Captain Thomas Matthews (Geoff Pierson) should be in Original Sin, as he was in most of Dexter‘s eight seasons and was good friends with Harry Morgan, but his role is currently being filled by Spencer. If Spencer is the serial killer and Dexter winds up killing him, it would be the perfect way to bring Matthews in and have him replace Spencer as Miami Metro’s captain. That twist would even work with Original Sin‘s early 1990s setting.

Episode #
Episode Title
Release Date & Time On Paramount+ With Showtime
Release Date & Time On Showtime

1
“And in the Beginning…”
December 13, 2024 @ 12:01 am ET
December 15, 2024 @ 10 pm ET

2
“Kid in a Candy Store”
December 20, 2024 @ 12:01 am ET
December 22, 2024 @ 10 pm ET

3
“Miami Vice”
December 20, 2024 @ 12:01 am ET
December 22, 2024 @ 10 pm ET

4
“Fender Bender”
December 27, 2024 @ 12:01 am ET
December 29, 2024 @ 10 pm ET

5
“F is for F***-Up”
January 3, 2025 @ 12:01 am ET
January 5, 2025 @ 10 pm ET

6
“The Joy of Killing”
January 10, 2025 @ 12:01 am ET
January 12, 2025 @ 10 pm ET

7
“The Big Bad Body Problem”
January 24, 2025 @ 12:01 am ET
January 26, 2025 @ 10 pm ET

8
“Business and Pleasure”
January 31, 2025 @ 12:01 am ET
February 2, 2025 @ 10 pm ET

9
“Blood Drive”
February 7, 2025 @ 12:01 am ET
February 9, 2025 @ 10 pm ET

10
“Code Blues”
February 14, 2025 @ 12:01 am ET
February 16, 2025 @ 10 pm ET

There is, of course, always the possibility that Captain Spencer won’t prove to be the main villain of Dexter: Original Sin season 1. Other characters, like Tanya Martin (Sarah Michelle Gellar), also have evidence suggesting they are the killer, and the show could always introduce a yet-unnamed character as the real murderer. Original Sin could also introduce Matthews by either having Spencer retire or by having him be killed by the real murderer. In short, though it’s a fairly convincing theory, there’s no proof yet that Captain Spencer is the real killer in Dexter: Original Sin.