Originally Posted by masuka
From what I remember it was in season 4.
Yeah: Season Four
His former love Debra Morgan begins an investigation into the past of the Ice Truck Killer. She learns of Laura Moser and through extensive research, finally discovers the truth about Dexter's relation to Brian as his actual biological brother. She confronts him about this, informing him of this information while also realizing that Brian was using her just to get to Dexter. The matter is never spoken of again following the Trinity Case,
though Brian is often mentioned in Dexter's thinking in relation to events where he deals with someone's brother and other characters often refer back to the case through the series.
And things carried on as usual until her shrink sessions. When you think about it, the storyline is getting too far fetched. His whole Serial Killing routine depends on him being a Low-profile Lab guy.
His whole Low profile shtick has been compromised. I mean he has a Police sister who was engaged to a serial Killer. Then his wife was killed by a serial killer. His Sister finds out that the serial killer she was engaged to was his biological brother, even though that never got revealed to the Press.
Either way, he shouldn't be able to walk around and continue with the killing spree as easily considering he and his sister were personally involved with two different serial killers. But oh well, it's television.