What item does Jerome (Vincent) leave behind at the murder scene?

Jerome, also known as Vincent, leaves behind an eyelash at the murder scene. This detail is crucial because it highlights the film's overarching theme of genetic identity and the importance placed on DNA in society. The eyelash serves as a biological marker in forensic evidence, and during the investigation, it becomes a key element that links Jerome to the scene of the crime. This aspect of the narrative underscores the tension between predestination and free will—Jerome’s struggle against a society that defines individuals strictly by their genetic makeup. By leaving behind something as small and seemingly insignificant as an eyelash, the film emphasizes the role of genetics in personal identity and fate, showcasing how even the smallest trace can determine one's future in a world obsessed with genetic perfection.