What is the name of the detective who suspects Dexter from early on?

The detective who suspects Dexter from early on is James Doakes. A detective sergeant at Miami Metro Homicide, Doakes immediately finds Dexter Morgan unsettling and notices that his calm, detached personality does not fit the image he presents.

During season 1, Doakes becomes especially suspicious of Dexter’s unusual interest in blood and crime scenes. He realizes that Dexter knows more about the Ice Truck Killer investigation than he should, and he begins watching Dexter closely. At this stage, Doakes does not yet know that Dexter is a serial killer, but he correctly senses that Dexter is concealing something serious.

Doakes’s suspicions grow in season 2 while he investigates Dexter’s past and behavior. He eventually finds Dexter’s box of blood slides and recognizes that Dexter may be the Bay Harbor Butcher. Dexter manipulates evidence to make Doakes appear responsible, leading to Doakes being blamed officially for the murders.

The other choices are colleagues who interact with Dexter but do not suspect him as early or as persistently. Doakes is the first major character to see through Dexter’s carefully constructed public persona.