This is a short video showing a dog’s reaction first to the lack of a specific person’s scent in the area and then to the presence of a specific person’s scent in the area. It also shows a dog’s indication that the suspect entered a building.
This is a short article on the beginning of the FBI’s Human Scent Evidence Team (HSET) that began in 2002.
https://archives.fbi.gov/archives/news/stories/2010/december/scent_122310/scent_122310
The two links below are to scientific papers written on the persistence and uniqueness of human scent as well as the uses of human scent in criminal investigations.
This final link is a scientific paper evaluating the performance of the Scent Transfer Unit (STU-100).