What crucial piece of evidence does Detective Hugo initially find to pursue Vincent?

The initial piece of evidence that Detective Hugo finds to pursue Vincent is indeed a strand of hair that does not match the genetic profile of Jerome. This evidence is critical as it highlights Vincent's identity as a genetic "invalid" who is using Jerome's identity to evade detection. The hair not matching Jerome’s genetic profile creates a tangible link that raises suspicions about Vincent’s true identity and nature. Such genetic evidence plays a vital role in the narrative by emphasizing the film's themes of genetic determinism and identity, as Vincent, despite being genetically inferior in society's eyes, seeks to transcend his limitations by assuming a different identity. The hair strand serves as a pivotal clue that propels the investigation forward and sets the stage for the ensuing conflict between genetic elitism and personal ambition.