They reveal in the third episode that the FBI agent leading the investigation had previously dated Aaron's ex. What they did NOT mention was that they met and started seeing each other while Aaron's ex was engaged to some other guy. They slept with each other for about a year, then she started seeing Aaron, and she shut down the FBI guy's attempt to start another affair while she was seeing Aaron (before then having an affair with ANOTHER guy, lmao, what a catch).
You're telling me FBI guy wasn't butthurt that the girl he liked picked Aaron over him and that's not why he zeroed right in on Aaron from the start and never let it go? And he was never even disciplined by the FBI.