Hot Take: Jake could find out Dexter is the BHB in a week OR LESS.

I’ll preface this by saying this would be after the BHB is discovered, they’re investigating who inside the NYPD is the BHB.

While he's goofy in his day-to-day behavior, the show repeatedly establishes that Jake is one of the NYPD's best detectives. He notices connections others miss, solves cold cases, and often identifies suspects through seemingly insignificant details.

Dexter is careful, but he's not invisible. Across the series, his victims overwhelmingly fit a specific profile. Many disappear shortly after coming under suspicion for violent crimes. He often has prior contact with them through police work. Several investigations get close to exposing him because of forensic or circumstantial evidence. Multiple characters independently become suspicious of Dexter, suggesting his operational security isn't flawless.

One of Jake's strengths is ignoring conventional wisdom when the facts don't fit. If a string of disappearances pointed toward someone "too clean" or "too helpful," Jake would likely investigate instead of dismissing the possibility.

Working as a blood-spatter analyst gives Dexter access to crime scenes, evidence, and investigative information. That also creates opportunities for timeline comparisons,
badge-access logs, case assignment overlaps, unexplained knowledge of investigations. A detective specifically looking for an insider could uncover suspicious coincidences.