Warning! This article contains SPOILERS for Dexter: Original Sin season 1, episode 6 & Dexter season 8.Dexter Morgan (Patrick Gibson) officially became a serial killer in Dexter: Original Sin episode 6, but it also changed details about his third kill that Dexter season 8 had already established. Dexter’s kill count is quickly growing as Original Sin progresses. In Original Sin episode 6, Dexter killed Levi Reed (Jeff Daniel Phillips), which marked his third kill. Since the FBI defines serial killers as murderers who have killed three or more people in separate events, Levi Reed’s death made Dexter an official serial killer. Though it was a special moment for Dexter, there was a problem: it retroactively changed the original series.

https://screenrant.com/dexter-original-sin-third-kill-levi-reed-identity-retcon-explainer/