Who turns out to be the detective leading the murder investigation?

The detective leading the murder investigation is Vincent's brother. This choice is significant because it adds a layer of complexity to the narrative and character dynamics within the film. The brother's position on the force creates a conflict of interest, as he is not only investigating a case involving his sibling but is also part of a society that places immense value on genetic engineering and the idea of "valid" versus "invalid" individuals. This relationship intensifies the themes of family loyalty and societal expectations portrayed in GATTACA. It highlights how personal relationships intersect with professional duties, emphasizing the film's exploration of identity and the impact of genetic predisposition on individual relationships and societal roles.