Factual error: Abby says she ran X-ray chromatography. There is no such thing. I assume she meant X-ray crystallography.
Factual error: Obviously written to make the story interesting, but Gibbs says that the first criminal caught by DNA was a Mafia don in Sicily. Well as anyone interested in forensics knows it was Colin Pitchfork in England.
Answer: I hadn't seen the backdoor pilots yet but while it wasn't explicitly stated, at least onscreen, I heard somewhere Vivian got either fired from NCIS due to jeopardizing a case, got resigned from the agency, or transferred to the FBI.
Raykvega423